Advanced rulebook

While most rules in Hearthstone are fairly easy to ascertain, when several effects, each with their own behaviours, are brought into conflict, things can get a little more complicated. The advanced rulebook offers a comprehensive explanation of the game's underlying processes, complete with examples and video references.


 * For information on the game's basic mechanics, see Gameplay, Minion, Abilities and Character.


 * If you are looking for a specific bug, see https://github.com/HearthSim/hs-bugs/issues.


 * For an in-depth reference to Hearthstone's internal program design, see Internal design.


 * For large changes to the game mechanics in Hearthstone, see Game Mechanics Updates.

Foreword
Because the advanced rulebook is written to document findings about how Hearthstone works, rather than the other way around, any given patch of Hearthstone may cause the advanced rulebook to have out-of-date information; Blizzard doesn't release a full changelog of bug/mechanic changes with each patch, and changes are often unintended. If you notice that something in the advanced rulebook is incorrect, please record what actually happens (such as by using https://obsproject.com/ ), upload the footage to Youtube and post a link on the talk page. Your contributions are always appreciated!

If you want to discuss advanced mechanics of Hearthstone in real time, join #hearthsim on http://irc.freenode.net/, where many scientists, bug testers and simulator writers hang out.

Keep in mind while reading this document that no interaction is hard-coded.

Sequences, Phases, Queues, Resolution
Definition: Player Actions are actions a player chooses to take on their turn while nothing is happening, such as attacking, playing a card, using your Hero Power and ending your turn. Definition: A Sequence is what begins when a Player Action is taken. A Sequence consists of one or more Phases, that are resolved in order. Definition: Phases are surrounding blocks created whenever one or more triggers/Events are raised. When the outermost Phase resolves, Hearthstone will run several Steps, including processing Deaths and updating Auras.


 * Hearthstone splits Turns into Sequences.
 * Player Actions (such as Combat, playing a card and ending the turn) form a Sequence of one or more Phases.

Examples


 * Sending a Character to attack another character creates a Sequence of two Phases - "Preparation" and "Attack".
 * Whenever a minion is summoned, a Sequence immediately begins with an "On Summon" and ends with an "After Summon" Phase.

Definition: An Event is any change in the game state. For example: Damage Event, Heal Event, Death Event, etc. (Additionally, all Phases have an associated Event(s).) Definition: A Trigger is something that reacts to an Event, i.e. triggered effects, Secrets and Deathrattles. Definition: Resolving means playing out all related consequences, one at a time.

Rule 1a: A Phase, trigger or Event is only resolved when all of its consequences are resolved. Rule 1b: When resolving simultaneous events, Hearthstone must resolve one event before it begins resolving the next. Rule 1c: Death is not checked during the standard resolution of Events.


 * When multiple events are awaiting resolution, the need to resolve an event before starting the next is a depth-first resolution. (If multiple events could be partially resolved, that would be breadth-first).
 * The moment a new trigger/Event is raised, Hearthstone begins to resolve it and immediately begins exploring its consequences, before resolving those remaining for the current trigger/Event. When a trigger/Event is resolved, Hearthstone picks up where it left off.
 * It seems that a trigger cannot be nested inside itself. Instead it works the skipped times as a compensation after all other consequences of it are resolved. See Trigger Re-entrancy Exploration.
 * If a player concedes in a Swedish style bracket, the result is .5 - .5 in player score.

Examples


 * You Flamestrike a Dragon Egg and Knife Juggler. The Dragon Egg immediately spawns a Black Whelp, causing the Knife Juggler to trigger and throw a knife (even though both are mortally wounded, because death is not checked during resolution). There are no further consequences, so the phase is resolved. Hearthstone kills both minions, removing them from the board.
 * Here is an example with Knife Juggler and Grim Patron
 * Here are three more examples of deeply nested triggers during the playing of a minion.  Here is an example of deeply nested triggers during Death resolution. Here is a very complicated series of triggers as a result of playing Feign Death in The Masked Ball.

Definition: A Queue is a sequential container where multiple simultaneous triggers or Events are held. Rule 2a: When we start to resolve a Phase or Event, A Queue is created and filled with all triggers that can respond, in order of play. Rule 2b: If multiple events are considered simultaneously (such as damage, healing, Deaths or 'return to hand' effects) they are Queued by order of play, then for each, triggers are Queued by order of play (as per Rule 2a). Rule 2c: A Queue becomes immutable once Hearthstone starts to resolve the first entry in it. No new entries can be added to the Queue after this point.


 * Order of play means the order the Entities each Event/trigger is associated with entered play, from oldest to newest.
 * Minions, Heroes, Weapons, Secrets, attached Enchantments and added Deathrattles are all Entities, and all exist in the same order of play list together.
 * Minions and Secrets summoned while resolving an Event cannot respond to Events that are in the middle of resolution, because their associated Queues are now immutable. However, they can Queue on any later Phases and Events created.
 * After Patch 9.2.0.21517 triggers in a Sequence that read 'After ...' can only work if they're valid when the Sequence starts.
 * After Patch 9.2.0.21517 consequences of Death can only work if their position and controller are valid before Death Creation Step.

Examples:


 * If you trade your Sylvanas Windrunner into your opponent's, the oldest Sylvanas will have its Deathrattle activate first.
 * If you Arcane Explosion three Grim Patrons and a Frothing Berserker, all the damage occurs, then each "On Damage" Event is resolved based on the order of play.
 * If a Mad Scientist dies and plays Duplicate, Duplicate does not get triggered in any queue of this Death Phase, for it is not present in Death Creation Step.
 * If you play a spell, Troggzor the Earthinator summons a Burly Rockjaw Trogg. The Burly Rockjaw Trogg does not trigger from the same spell because the consequences of playing the spell have already begun resolving.
 * Your Grand Archivist steals an enemy minion with Shadow Madness at the end of your turn. This minion is not returned immediately, but at the end of your opponent's next turn.

Notes and exceptions:
 * Some triggers have a Priority that supersedes order of play and always triggers earlier or later. One example is Redemption which always Queues last.

Rule 3: Once a Phase begins, nested Phases with their own Queues may start and end inside of it, but only the outermost Phase ending initiates the Death Creation Step.


 * This means that you will NEVER see an Entity be killed in the middle of a Phase, no matter how complexly nested it becomes.
 * This also means that even though Sequences like summoning a minion have many Phases, if it occurs as a consequence of another Player Action instead of being due to playing a card, the entire thing happens before any Deaths occur.

Examples:
 * You play Knife Juggler then Dr. Boom. When Dr. Boom's Battlecry (a Phase) begins, Boom Bots are summoned, and each one triggers the Knife Juggler to throw knives at enemy minions. Even though minion summoning is a Sequence of multiple Phases, we are already inside of a Phase, so the entire Battlecry remains inside of one Phase, rather than starting and stopping. Finally when the Battlecry resolves, Deaths are processed and the Deathrattles go off.
 * You play three Unstable Ghouls. Your opponent plays an Acolyte of Pain, damages it to 1 Health and casts Flamestrike. All three Unstable Ghouls's Deaths are considered in one Phase, meaning that the Acolyte of Pain is hit, triggered and draws three cards, despite being mortally wounded after the first Deathrattle. Finally the Phase ends and the Acolyte of Pain is killed.
 * Your opponent has a Cult Master and Novice Engineer both at 1 Health. You play a Mad Bomber, and both are reduced to 0 Health during the Battlecry Phase. Regardless of order of play, and regardless of the order the minions are mortally wounded by the bombs, the Cult Master cannot draw a card from the Novice Engineer dying because both deaths occur simultaneously after the Phase ends.

Exceptions:


 * There are three effects in the game that break this rule and kill minions in the middle of a Phase. For more information, see the Forced Death Phase section.

Rule 4a: After the outermost Phase ends, Hearthstone does an Aura Update (Health/Attack), then does the Death Creation Step (Looks for all mortally wounded (0 or less Health)/pending destroy (hit with a destroy effect) Entities and kills them, removing them from play simultaneously), then does an Aura Update (Other). Entities that have been removed from play cannot trigger, be triggered, or emit auras, and do not take up space. Rule 4b: Besides, whenever a minion is summoned (but not played), Hearthstone updates both kinds of Auras. Rule 4c: Some Auras that are known to update in Aura Update (Other) is as follows: Baron Rivendare, Auchenai Soulpriest, Brann Bronzebeard, Mal'Ganis's Immune effect, Prophet Velen, Violet Illusionist, Drakkari Enchanter, The Four Horsemen (Hero Power). Rule 4d: Enchantments apply and modify Health/Attack/Mana costs the moment they are attached. However, during Aura Update (Health/Attack), the Enchantment List is re-processed and Health/Attack Auras, having a priority later than Health/Attack Enchantments, will be moved to the end of the Enchantment List during this timing. (However, Mana Cost Auras have no special priority compared to Mana Cost Enchantments.)


 * When a minion is played, its Aura is sent for the first time before the Battlecry Phase. When a minion is stolen, it does not start emitting its aura until the outermost Phase ends, unless a new minion is summoned.
 * Until the moment it is removed from play, the Entity can be brought back from 0 or less Health by healing or Health buffs, and still shares auras. This is important when multiple minions are attacked simultaneously, or when a hero dies in the same Sequence as minions with Deathrattles.
 * If you kill a minion with an aura and a minion with a Deathrattle simultaneously, non-Health effects of the aura are not active during the following Death Phase because the minion is removed from play. However, Health effects of the aura will be active, because Hearthstone does not recalculate Health changes after the minions are killed, unless a new minion is summoned.  However, a health-granting aura such as Mal'Ganis can save a minion from dying, even if it enters play the same Phase the other minion was mortally wounded, because the aura recalculation is done before the Death Creation Step.
 * Auras are not recalculated due to minions leaving play or due to minions being stolen in the middle of a Phase..
 * Brann Bronzebeard, Baron Rivendare and Drakkari Enchanter check before an Event starts. This means if one Battlecry/Deathrattle/End of turn effect summons them, it will not trigger again. But Deathrattles/End of turn effects that follow can benefit, for Aura (Other) is updated when you summon them.
 * Some auras in the game have a higher Priority than others. This means that order of play does not matter if one aura's Priority is simply higher. For example, Summoning Portal's aura always comes first (meaning also having a Mechwarper makes Harvest Golems cost 0 mana, regardless of play order) and Lightspawn's and 'Tar' minions' auras always come last.
 * Despite not visually updating, enchantments take effect the moment they are created.

Examples:


 * You play a Stormwind Champion, Explosive Sheep and Mana Wyrm. You damage the Champion and Sheep to 1 Health, with the Mana Wyrm at 4 Health (current and maximum). You play Cone of Cold, simultaneously killing and removing from play the Champion and Sheep. Because only non-Health effects of auras are recalculated after the Death Creation Step, in the following Death Phase, the Mana Wyrm goes from 4 Health to 2, not 3 to 1, and ends as an x/2 instead of an x/1.
 * You play an Auchenai Soulpriest and a Zombie Chow, damage the Auchenai Soulpriest to x/4 and then cast Circle of Healing. After the Spell Text Phase ends, both the Soulpriest and Zombie Chow are killed and removed from play. Because non-Health effects of auras end following the Death Creation Step, the Zombie Chow heals your opponent for 5, instead of damaging them for 5.
 * You have a Cult Master and a Bloodfen Raptor. Your opponent plays Flamestrike. The Phase in which the spell is cast resolves, and both minions are killed simultaneously. The Cult Master cannot trigger on the Bloodfen Raptor's Death because it is removed from play at the same time.
 * Your hero is at 2 Health and attacks a Zombie Chow with his Fiery War Axe. You and the Zombie Chow die and are removed from play - it is too late for the Zombie Chow's Deathrattle to save you, and you lose the game. Similarly, if you suicide into an Abomination, the Deathrattle of which kills a Zombie Chow, you are already dead and gain no healing.
 * Your hero is at 5 Health. You cast Hellfire against an enemy Leper Gnome and Zombie Chow. Both enemy minions die simultaneously, and regardless of order of play, you are hurt for 2 Health and healed for 5 Health, ending at 5 Health once more before Hearthstone checks for new Deaths.
 * You play an Abomination and Mal'Ganis (order irrelevant), weaken both to 3 Health and cast Hellfire. The Hellfire does not damage you, but mortally wounds both minions. After the Spell Text Phase ends, both minions are removed from play and you stop being Immune, so when the Abomination's Deathrattle goes off you take 2 damage.
 * You have a Stormwind Champion and a damaged 5/1 minion and Redemption is in play. Your opponent casts Fireball on your Stormwind Champion, reducing it to 0 Health. Because we run Aura Update (Health/Attack) before the Death Creation Step, Stormwind Champion's aura is still in effect during the following Death Phase, where Redemption triggers and summons a new 6/1 Stormwind Champion. In the next Aura Update (Health/Attack) the 5/1 minion remains a 5/1 minion because as far as Hearthstone is concerned, the aura never left or got added again. (If there was a timer at which the aura was found to be missing, it would have been dropped to a 4/1, then buffed to a 5/2.)
 * You have two Auchenai Soulpriests and play a Zombie Chow, a Moat Lurker targeting one Auchenai, another Zombie Chow, then use AoE to clear your board. First all minions left play, then first Zombie's deathrattle restores 5 health for enemy hero. Then an Auchenai is summoned causing Aura Update. So the second Zombie deals 5 damage to enemy hero.
 * Your opponent has Sylvanas Windrunner and casts Ancestral Spirit on it. You play Baron Rivendare and Sylvanas then exchange Sylvanas. Enemy Sylvanas steals your Rivendare, and Ancestral Spirit summons Sylvanas causing Aura Update. Then another Sylvanas is summoned and your Sylvanas's deathrattle can only steal one enemy minion.
 * You play Krul the Unshackled to summon Demon I, Unlicensed Apothecary, Demon II, Mal'Ganis and Demon III (in this order) from hand. Your hero only takes 5 damage for Demon II.
 * You have The Four Horsemen (Hero Power), 3 of the Horsemen and an oldest Sylvanas Windrunner. Your opponent has another Horseman and a newest Sylvanas. You trade your Sylvanas into your opponent's. Due to the lack of Aura Update (Other), controlling all 4 Horsemen momentarily won't have you win the game.

Rule 5: While characters cannot be killed in the middle of a Phase, 'negative' (damaging/destroying/hindering/misdirecting) triggers ignore mortally wounded and pending destroy characters. Also, Secrets abort if their specific target is mortally wounded, pending destroy or they otherwise cannot meaningfully trigger. However, 'beneficial' (healing/buffing) triggers count mortally wounded, and AoE effects count mortally wounded. Rule 5b: For the purposes of 'if it survives'/'if that kills it' effects, mortally wounded and pending destroy Characters are considered to not have survived/to have been killed, even though they are (for now) still in play. If the target is in the Graveyard, it is also considered to have been killed.


 * Knife Juggler is an example of a negative trigger that ignores mortally wounded and pending destroy characters. If all targets are mortally wounded or pending destroy, it aborts.
 * Freezing Trap is an example of a Secret that aborts if its target is mortally wounded or pending destroy. Similarly, Noble Sacrifice aborts if there is no space for the Defender it would summon, and thus no way to trigger.
 * Dark Cultist's Deathrattle is an example of a positive trigger that considers mortally wounded characters valid!
 * Grim Patron, Slam and Blood To Ichor's conditions are only true if the relevant minion is not mortally wounded or pending destroy, such as due to Acidmaw. (Conversely, Mortal Coil and Bane of Doom's conditions are true if the relevant minion is mortally wounded or pending destroy.)

Examples:


 * If you play two Knife Jugglers and then Unleash the Hounds, no enemy will be reduced to lower than 0 Health by a knife, because Knife Juggler is a damaging trigger.
 * If you play Explosive Trap then Freezing Trap, your enemy's Novice Engineer attacking into it will trigger the Explosive Trap and be reduced to -1 Health. The Freezing Trap is a hindering Secret and thus aborts having no target it considers valid.
 * Misdirection and Clumsy effects like Ogre Brute, being hindering triggers, pretend mortally wounded characters don't exist and can't redirect an attack onto one.
 * If you play an Explosive Sheep, Dark Cultist and Chillwind Yeti and your opponent plays Flamestrike - First, the Explosive Sheep and Dark Cultist's Deaths are resolved in a single Phase. First, the Explosive Sheep goes off and mortally wounds the remaining Chillwind Yeti - but the Dark Cultist doesn't ignore mortally wounded characters, and the Chillwind Yeti is buffed and survives as a 4/2.
 * If you play an Auchenai Soulpriest, Acolyte of Pain buffed to 1/5 and two Unstable Ghouls, then play Circle of Healing (killing both Unstable Ghouls and reducing the Acolyte of Pain to a 1/1), in the following Death Phase the two Unstable Ghouls, by Rule 5, will both hit the Acolyte of Pain and cause it to draw a card, finally being removed from play as a 1/-1 with 3 total cards drawn.
 * If you play a Baron Geddon followed by a Healing Totem, then end your turn, during the End of Turn Phase, Baron Geddon reduces the Healing Totem to 0 Health, then the Healing Totem heals itself for 1, and when we reach the Death Creation Step, the Healing Totem remains alive. This also works, for example, with Imp Master and Healing Totem.
 * If you play Brann Bronzebeard and Stampeding Kodo, the Stampeding Kodo cannot pick the same target twice, since it ignores pending destroy minions.
 * Poisonous on minions resolves in a queue with higher priority, and it stops Grim Patron spawning regardless of Dominant Player. However, Poisonous on weapons and Acidmaw can never stop Grim Patron spawning. This might be a bug.
 * If you use Mortal Coil on a minion while Acidmaw is in play, because the damage is resolved before the condition is checked, the pending destroy target is considered to have been killed and a card will be drawn.
 * You have The Four Horsemen (Hero Power), 3 of the Horsemen and Knife Juggler, but your hero is at only 1 health. Your opponent has an empty board with Eye for an Eye. You summon the fourth Horseman from your Hero Power, setting enemy hero pending destroy. Knife Juggler will hit no one as there is no valid target, preventing you from being killed.

Rule 6: Subsequent Phases of a Sequence will not run if a subject is required but is no longer in play. However, this is the only requirement - If the target of the action has some requirements beyond that, the requirements are not re-checked.


 * The subject of casting a spell doesn't exist - so Counterspell only stops Overload and Spell Text Phase.
 * The subject of playing a minion is the minion itself.
 * The subjects of combat are the attacker and defender.

Examples:


 * You attack with a Novice Engineer into Explosive Trap. By the time the Combat Phase is reached, the Novice Engineer has been killed and removed from play, so no combat occurs.
 * You attack with a Truesilver Champion into a Novice Engineer. During the Preparation Phase, an allied Shadowboxer triggers and mortally wounds the Novice Engineer. By the time the Combat Phase is reached, the Novice Engineer has been killed and removed from play, so no combat occurs.
 * You have a Knife Juggler and play an Elven Archer into an Unstable Ghoul with 1 Health left. After the Battlecry Phase, the Deathrattle kills the Elven Archer. By the time the Knife Juggler would trigger, the Elven Archer has been killed and removed from play.
 * You cast Shadow Word: Pain on a Burly Rockjaw Trogg. It gets buffed to 5 attack before the spell's text begins. This wouldn't be a valid target before, but the spell successfully destroys the Burly Rockjaw Trogg.
 * A Boulderfist Ogre is next to a Dire Wolf Alpha and thus buffed to 7 attack. You play a Big Game Hunter between the two and target the Boulderfist Ogre. By the time the Battlecry goes off, the Boulderfist Ogre is a 6 attack minion, but it is still destroyed.

Exceptions:


 * If you cast a targeting spell, but the spell's target is removed from play before the spell text begins, it still goes off anyway (this matters, for example, with spells like Drain Life that have side-effects).
 * Cards which target 'if you're Holding a Dragon' (Rend Blackhand, Blackwing Corruptor, and Book Wyrm) check their requirements a second time during the Battlecry Phase, and will fail to have effect if their owner lacks a Dragon at this point, even if they were given a target.

Rule 7: If one or more Deaths happened after the outermost Phase ended, a new Phase (called a “Death Phase”) begins, where Deaths are Queued in order of play. For each Death, all Death Event triggers (Deathrattles, on-Death Secrets and on-Death triggered effects) are Queued and resolved in order of play. When this is complete, the Death has been resolved.


 * After Patch 9.2.0.21517 consequences of Death can only work if their position and controller are valid before Death Creation Step.
 * Besides Redemption, which has a special Priority that makes it always queue last, all triggers follow order of play exactly, however mingled that makes them get.

Examples:


 * You have a Duplicate put into play, a Sludge Belcher injured to 4 Health and Dark Cultist, played in that order. Your opponent casts Flamestrike. In the Death Phase that follows, we consider first the Sludge Belcher's Death, queuing Duplicate then its Deathrattle. They go off in order, giving you two Sludge Belcher cards then summoning a Slime. Now we consider the Dark Cultist's Death, queuing its Deathrattle. It triggers, buffing the Slime to 1/5. If the minions were played the other way around, the buff would have no target at time of activation and the Slime would remain at 1/2 (and you would be given two Dark Cultist cards instead).
 * You play a Mad Scientist then a Bloodfen Raptor. Your opponent casts Flamestrike. In the Death Phase that follows, we consider first the Mad Scientist's Death, queuing its Deathrattle. It goes off and puts into play a Duplicate. Now we consider the Bloodfen Raptor's Death. Since Duplicate is not present in Death Creation Step, it remains hidden.

Rule 8: A Death Phase can have yet another Death Phase after it. This process repeats forever until no new Deaths occur, and we can finally move on to the next intended Phase in the Sequence.

Examples:


 * You have an Explosive Sheep and an Abomination. Your opponent casts Consecration. This creates a Death Phase to resolve the Death of the Explosive Sheep. Its Deathrattle triggered, after that Death Phase ends, the Abomination is dead and a second Death Phase is created to resolve its Death.

Exceptions:


 * There are four effects in the game that break this rule and kill minions in the middle of a Phase. Since it's in the middle of a Phase, when this “Forced Death Phase” ends, a new Death Phase can't be made to resolve new Deaths, and they remain unresolved for now. For more information, see the Forced Death Phase section.

Rule 9: Finally when the Sequence ends and the player gets control again, Hearthstone checks if the game has ended in a Win, Loss or Draw.


 * This means that if one Hero dies, the game does not immediately end - further triggers in the current Sequence may lead to the other Hero also dying.

Examples:


 * The enemy hero is at 1 Health and you aim an Elven Archer's Battlecry at them. This kills them, but later your allied Knife Juggler still triggers. This can cause the game to instead tie, for example if the knife kills an Abomination which kills your hero.

Exception: Hearthstone decides the game as a win/loss/draw between the Preparation Phase and Combat Phase of attacking with a character. This is the only known exception.


 * You are at 2 Health and you attack with a Snowchugger into Explosive Trap. Preparing to attack is a Phase, containing the triggering of the Explosive Trap. During the Death Creation step following the Phase, your hero is killed (a Death Phase is made to resolve the Death of your hero, but there are no Death Event triggers so nothing happens). After that, Hearthstone checks if the game is over, and declares a Loss for you. (Note that the Snowchugger never finished its attack!)

Rule 10: Minions and effects have no memory of earlier board state. The moment an event takes place the board state is updated. Whenever a Queue is populated or an effect resolved (or continued), the most up to date board state is used.
 * One consequence of Rule 10 is that minions only know who their current controller is - they have no memory of their original controller. In MtG terms, this means owner = controller.
 * This also applies to effects that trigger or end at a specific player's start or end of turn. If they are stolen, then they forget their previous owner, and use the timing of their new owner.
 * The exception is Blessing of Wisdom, which draws cards for its caster no matter how many times it is stolen. (However, its CONTROLLER tag is still changing values, like any other stolen enchantment attached to a stolen entity.) Shadow Madness also remembers which side it 'should go back to' even if stolen by Sylvanas Windrunner in the mean time.

Examples:


 * If you play a minion, and it is stolen by Sylvanas Windrunner at any point of the 'Playing a minion Sequence' (such as before the Battlecry or after the Battlecry), the remaining Phases will be carried out as though the new owner had played the minion him/herself.
 * If you play a Dragon Egg then Mad Bomber and the first bomb hits the Dragon Egg, the on-damage trigger immediately runs, the Whelp immediately spawns, and the second and third bomb may hit the Whelp as though it always existed.
 * Any time multiple minions with their own Deathrattles die simultaneously, the Deathrattles are resolved in order of play, and the outcome of each Deathrattle can be effected by the next Deathrattle, such as the Damaged Golem from a Harvest Golem being damaged by an Explosive Sheep dying later. In addition, secrets like Avenge will Queue for a Death Event if, at the start of a Death Event, a friendly minion is on the board - even if it was added by a previous Deathrattle, and didn't exist at the start of the Death Phase.
 * If your opponent plays Conceal, which will end at the start of their next turn, and you use Sylvanas Windrunner to steal one of their minions, the stolen minion will remain in stealth until the start of your next turn.
 * If you play Nightmare on a minion controlled by either player, the Nightmare Enchantment initially has you as its controller, and will trigger in your next Start of Turn Phase. However, whenever the minion changes controllers, the controller of the attached Nightmare becomes the same as the minion's new controller, so it will now trigger in the Start of Turn Phase of that controller.
 * If you play Kill Command with a friendly Beast in play, but Violet Teacher triggering Knife Juggler killing Explosive Sheep kills your friendly Beast before the Spell Text Phase begins, the most up to date board state is used and 3 damage is dealt, not 5.

Rule 10b: Triggered effects with a condition check their condition at these timings: Pre-check timing, Queuing and Triggering.
 * Only triggers in After Play Phase and Death Phase apply a pre-check - see Rule 2.
 * Targeting effects with a condition (like targeting Battlecries and Spells) work differently - see Rule 6.

Examples:


 * If you play a Faceless Manipulator and it transforms into anything that isn't an unsilenced Battlecry minion, your Rumbling Elemental will not trigger. This is because the played minion is no longer a Battlecry minion. Similarly, if you play Lord Jaraxxus, your Rumbling Elemental will not trigger. This is because the played minion is no longer in play.
 * If you have 1 minion and play Dr. Boom, your opponent's Sacred Trial will not trigger because it's not valid at pre-check timing.
 * If you have a Djinni of Zephyrs and play a Take control spell (Mind Control, Shadow Madness, Entomb, or Potion of Madness) on an enemy minion, your Djinni of Zephyrs doesn't trigger either.

Death Phases and consequences of Death
 (This section has a video accompaniment! Check out the 20 minute long video [Hearthstone Science] When Do Minions Die? here: https://www.youtube.com/watch?v=H3d_qlm4Xws ) 

Let's recap the Rules that are relevant to Death and processing it:

Rule 3: Once a Phase begins, nested Phases with their own Queues may start and end inside of it, but only the outermost Phase ending begins the Death Creation Step.

Rule 4a: After the outermost Phase ends, Hearthstone does an Aura Update (Health/Attack), then does the Death Creation Step (Looks for all mortally wounded (0 or less Health)/pending destroy (hit with a destroy effect) Entities and kills them, removing them from play simultaneously), then does an Aura Update (Other). Entities that have been removed from play cannot trigger, be triggered, or emit auras, and do not take up space. Rule 4b: Besides, whenever a minion is summoned (but not played), Hearthstone updates both kinds of Auras. Rule 4c: Some Auras that are known to update in Aura Update (Other) is as follows: Baron Rivendare, Auchenai Soulpriest, Brann Bronzebeard, Mal'Ganis's Immune effect, Prophet Velen, Violet Illusionist, Drakkari Enchanter, The Four Horsemen (Hero Power). Rule 4d: Enchantments apply and modify Health/Attack/Mana costs the moment they are attached. However, during Aura Update (Health/Attack), the Enchantment List is re-processed and Health/Attack Auras, having a priority later than Health/Attack Enchantments, will be moved to the end of the Enchantment List during this timing. (However, Mana Cost Auras have no special priority compared to Mana Cost Enchantments.)

Rule 7: If one or more Deaths happened after the outermost Phase ended, a new Phase (called a “Death Phase”) begins, where Deaths are Queued in order of play. For each Death, all Death Event triggers (Deathrattles, on-Death Secrets and on-Death triggered effects) are Queued and resolved in order of play, then the Death is resolved.

Rule 8: A Death Phase can have yet another Death Phase after it. This process repeats forever until no new Deaths occur, and we can finally move on to the next intended Phase in the Sequence.

Notes:
 * An on-Death triggered effect triggers for a Death so long as its bearer is not dead yet and thus still in play. (Don't forget that mortally wounded and pending destroy are ONLY converted into dead once the outermost Phase ends!)
 * An on-Death Secret triggers for a Death so long as it existed at pre-check timing AND its queuing conditions were satisfied (in the case of Avenge for example) at the time the Queue was created.

Exceptions:


 * Redemption has a Priority that means it always queues last, regardless of order of play. (It still queues with the first Death it can.) This prevents the minion's Deathrattle from affecting the newly revived copy, such as if it was an Explosive Sheep.

Examples:


 * Your opponent plays a Deathlord. You damage it to a 2/2 then play a Bloodfen Raptor and Avenge. Your opponent trades the Deathlord into your Bloodfen Raptor, killing both. In the following Death Phase, the Deaths are considered in order - first the Deathlord (putting into play for you a River Crocolisk and finally the Bloodfen Raptor (triggering the Avenge, as at the moment of the queuing you have an alive minion for its target). If the Deathlord was second in order of play, not first, the Avenge would not go off as it would not have a valid target, THEN you would get a new minion.
 * You play Ancestral Spirit on an Explosive Sheep and your opponent pings it. Because the Ancestral Spirit entered play second, in the following Death Phase, the 2 damage Deathrattle occurs THEN a new Explosive Sheep is summoned.
 * You play a Piloted Shredder and Explosive Sheep. Your opponent plays Flamestrike. In the following Death Phase the Deaths are considered in order - first the Piloted Shredder (summoning a new Explosive Sheep) then the Explosive Sheep (mortally wounding the new Explosive Sheep). There are new Deaths, so once again a Death Phase is queued, where the new Explosive Sheep's Deathrattle resolves and also deals 2 damages to minions. If in this scenario your Explosive Sheep was played first, the newly summoned minion from Piloted Shredder would be undamaged.
 * You play an Explosive Sheep and a Cult Master. Your opponent pings the Explosive Sheep. In the following Death Phase the Explosive Sheep's Death is considered, and its Death Event triggers are queued in order - first the Explosive Sheep's Deathrattle, which mortally wounds the Cult Master, then the Cult Master's on-Death trigger, which draws a card. Finally, a new Death Phase begins where the Cult Master is killed and its Death Event triggers resolved. If Death happened instantaneously, the Cult Master would not have drawn once, but since it is delayed, he remained alive for the Phase's duration.
 * You play a Cult Master and Bloodfen Raptor in that order and have Redemption in play. Your opponent plays Flamestrike. A Death Phase begins where we consider first the Death of the Cult Master, triggering Redemption and summoning a new Cult Master, then the Death of the Bloodfen Raptor, where the newly summoned Cult Master cannot trigger.
 * You play Feugen and Stalagg and weaken both to 4 or less Health. Your opponent casts Flamestrike, mortally wounding both during the Spell Text Phase. After that Phase ends, during the Death Creation Step, both minions are Killed and removed from play. In the subsequent Death Phase, we consider the Deaths in order - but since both Deaths already happened, you get two copies of Thaddius, not one.

Start and end of turn
Now that we know the 10 Rules, we can very simply describe what happens between turns:


 * End of Turn Phase: All 'end of turn' Triggers (as well as the special case Shadow Madness ) are Queued and resolved.
 * Hearthstone checks for win/loss/draw. The game is a draw if turn 89 (aka Player 1's 45th turn) just ended. It is now your opponent's turn. Hearthstone wears off expired enchantments (like Ice Block's effect and Bloodlust's effect), resets all counters related to 'this turn' (such as Deaths and cards played this turn), fills your opponent's mana, flips which player's weapons are sheathed/unsheathed, flips which player's Secrets are active, unflips your opponent's Hero Power and removes exhaustion from all characters.
 * Start of Turn Phase: All 'start of turn' Triggers (including Corruption and Nightmare and Competitive Spirit ) are Queued and resolved. Shifter Zerus also triggers here.
 * Hearthstone checks for win/loss/draw.
 * Draw a Card Phase: Your opponent draws one card, and any consequences are resolved now.
 * Hearthstone checks for win/loss/draw.

Notes:


 * Enchantments that trigger at the start or end of turn Queue in order of play alongside typical triggers. Enchantments that simply end without any side-effects end 'between turns' instead.
 * Echoing Ooze works by making an end-of-turn triggered effect on itself that can be doubled by Brann Bronzebeard. (Faceless Manipulator and Mirror Entity can copy this.)
 * Shadow Madness works by timing its enchantment to end in order of play, so it can occur before and after end-of-turn triggers.

Examples:


 * You play Ragnaros the Firelord and cast Shadow Madness on an enemy minion. They are queued in this order, and thus Ragnaros the Firelord damages an enemy character, THEN the stolen minion is returned.
 * You play Shadow Madness on an enemy 1 Health Imp Master. Because Shadow Madness queues second, you get Imp Master's end of turn trigger, THEN the minion is returned, THEN the Phase ends and Imp Master dies on your opponent's side of the board.
 * You play Ragnaros the Firelord and then your opponent plays Gruul. When you next end your turn, Ragnaros the Firelord may damage your opponent's Gruul to 8/0, but the Phase is not over - Gruul triggers and buffs himself to 9/1, and survives the Phase.
 * You play Sneed's Old Shredder and your opponent plays Ragnaros the Firelord. During the End of Turn Phase, Ragnaros hits and mortally wounds your Sneed's. In the Death Phase afterwards, Sneed's Deathrattle spawns a Kel'Thuzad. However, Kel'Thuzad does not activate and revive your Sneed's, because the End of Turn Phase is already over.
 * You play Kel'Thuzad and suicide your Emperor Thaurissan. At the end of your turn, Kel'Thuzad revives Emperor Thaurissan, but Emperor Thaurissan does not then trigger, because the Phase's Queue is immutable.
 * You play Doomsayer then Demolisher. At the start of your next turn, Doomsayer goes off first, but the Demolisher has not yet been removed from play, and will deal 2 damage one last time before the Phase ends and it is removed from play.
 * Your opponent has Emperor Thaurissan. You play Sylvanas Windrunner and cast Power Overwhelming on it. At the end of your turn, the Power Overwhelming is Queued and Sylvanas is marked pending destroy. After that phase ends, a Death Phase begins where Sylvanas's Deathrattle steals Emperor Thaurissan. He does not trigger for you, because the phase where he would trigger is already over.
 * Your opponent has a Repair Bot (which triggers to heal during the End of Turn Phase). You cast Shadow Madness on it, then Faceless Manipulator on the copy. During the End of Turn Phase, we see all triggers end in order of play - Repair Bot #1's trigger, Repair Bot #1's Shadow Madness ends, Repair Bot #2's trigger, Repair Bot #2's Shadow Madness ends.
 * You steal your opponent's Emperor Thaurissan with Shadow Madness (perhaps via shrinkmeister). During the End of Turn Phase, triggers end in order of play, so you get 1 mana cost reduction from Thaurissan before he is returned to your opponent.
 * You play Kel'Thuzad and play Power Overwhelming on a separate minion. Regardless of order of play, both triggers are queued during the End of Turn Phase, but the death does not occur until the following Death Phase, so Kel'Thuzad cannot revive minions killed during the End of Turn Phase.

Playing a spell
When you play a spell, the following Sequence takes place:


 * 1) The card is removed from your hand and enters Play and its Mana cost is paid. If it targets, the target is remembered (and its validity is not checked again). (If Bloodbloom or Cho'Gall is out, you take damage instead. This damage is resolved immediately, e.g. for Floating Watcher.)
 * 2) On Play Phase: All triggers on playing a card/casting a spell/playing a Secret Queue and resolve here, such as Unbound Elemental, Questing Adventurer, Mana Wyrm, Burly Rockjaw Trogg, Secretkeeper and Violet Teacher. Counterspell also triggers here - Counterspell will not stop triggers in this Phase, but will prevent the Overload and Spell Text Phase and send the spell to the Graveyard. Preparation/Kirin Tor Mage also triggers here. Dragonkin Sorcerer, Eydis Darkbane and Fjola Lightbane also trigger here.
 * 3) Spell Text Phase: First Spellbender and Mayor Noggenfogger queue and resolve. Then the entirety of the spell text takes place in one Phase. All triggers to its events are fully resolved. (If it is a Secret or Quest, nothing happens here - it already entered play.)
 * 4) After Spell Phase: Wild Pyromancer, Flamewaker and Djinni of Zephyrs Queue and resolve here.   Note that after Patch 9.2.0.21517 these triggers can only work if they're valid when the Sequence starts.
 * 5) Hearthstone checks for win/loss/draw.

Notes:


 * Counterspell used to stop all subsequent Phases, but not triggers in the same Phase, until Patch 9.2.0.21517. After this patch, the full Sequence is allowed to continue.
 * If the spell has a targeting condition (such as Shadow Word: Pain), but the condition is no longer true by the time the Spell Text Phase is reached, the targeting condition is not re-checked and the spell proceeds.  Mayor Noggenfogger only chooses the target that is valid at his timing.
 * If the spell requires a target, and the target is removed from play during an intermediate Phase, the spell goes off anyway. It will affect its target in the Graveyard Zone, which mostly does nothing, but side-effects and second steps may still go off.
 * If the spell has multiple steps (e.g. Blizzard, Light of the Naaru, Mortal Coil, Holy Nova ), triggers can occur between steps, regardless of whether the card's text uses 'and' or 'then'. Swipe used to be one of these, but its behaviour was changed in Patch_2.7.0.9166 (Tavern Brawl patch). For more information see Bugs.
 * A small number of spells process Deaths in the middle of the Spell Text Phase. These are Reincarnate and Poison Seeds. For more information see the Forced Death Phase section.
 * Secrets played from the hand enter play before the On Play Phase, and the effect of Counterspell is to send them to the Graveyard. (Both these statements are also true for regular Spells, by the way - just that a spell doesn't maintain physical presence while it's in play.)
 * If a spell requires a certain number of minions to be in play to be played (for example, Cleave requires two enemy minions to be played) and by the time it resolves it could no longer be played, the condition is not re-checked - the spell will do as much as possible (for example, Cleave will hit one minion if only one is left).

Examples:


 * You play Violet Teacher then cast Power of the Wild. The new Violet Apprentice appears before the Spell Text Phase and gets the +1/+1.
 * You play Violet Teacher and Knife Juggler then cast Swipe on an enemy minion with 1 Health. During the On Play Phase, Violet Teacher summons a Violet Apprentice, which triggers Knife Juggler and mortally wounds the enemy. By the time the Spell Text Phase begins the target has been removed from play, but the Swipe still goes through its spell text and deals 1 AoE damage to all enemy characters. A similar setup using Cone of Cold instead will show that the Cone of Cold hits and freezes nothing, since its target, now in the Graveyard, has no adjacent minions on the playing field.
 * You cast Blizzard on a Dragon Egg. It triggers on the 2 damage, summons a Whelp, and then the AoE Freeze occurs, freezing the Whelp. This is officially not a bug.
 * Your enemy plays Counterspell. You play an Unbound Elemental and Tunnel Trogg then Lightning Bolt. Unbound Elemental gains a buff AND Counterspell goes off. You gain no Overload, so Tunnel Trogg does not trigger.
 * Your enemy plays a River Crocolisk. You play a Flamewaker then Frostbolt the River Crocolisk. By the time the Flamewaker triggers, the River Crocolisk has been removed from play and so all the damage goes to the enemy hero.
 * Your enemy has many minions, you have seven Flamewakers and cast Arcane Intellect. By Rule 5, no Flamewaker will overkill any enemy minion, similar to how multiple Knife Jugglers work.
 * You are at 3 Health and your opponent is at 1 Health. You have a Violet Teacher and Knife Juggler. You play Hellfire. Before the Spell Text Phase, a Violet Apprentice is summoned and the Knife Juggler kills your opponent. However, the Sequence continues, and you kill yourself with the Hellfire cast, and the game ends in a draw.

Playing a weapon
When you play a weapon, the following Sequence takes place:


 * 1) The card is removed from your hand and its Mana cost is paid. The card enters Play as a weapon. If it targets, the target is remembered.
 * 2) On Play Phase: All triggers on playing a card Queue and resolve here, such as Questing Adventurer, Fel Reaver and Illidan Stormrage.
 * 3) Equipping Phase: The Battlecry of your new weapon (if any) is resolved. Then Buccaneer triggers. Finally your old weapon is destroyed and removed from play. The Deathrattle of your old weapon (if any) and Grave Shambler are resolved in the order of play.
 * 4) After Play Phase: Voidform's refreshing effect resolve here.
 * 5) Hearthstone checks for win/loss/draw.

Notes:


 * Your old weapon isn't removed immediately your new weapon enters play, and you are regarded as equipping two weapon simultaneously during this time. Both weapons' effects can trigger even if they are of the same name.
 * Your new weapon's Battlecry can be affected by your old weapon.
 * Before Patch 9.0.0.20457 there is no concept of pending destroy coded for Weapons. This means that the spells Sabotage and Blade Flurry and the Battlecries of Acidic Swamp Ooze and Harrison Jones, and even the very basic action of equipping a weapon over a weapon must forcefully move the weapon to the Graveyard, rather than letting it naturally happen at the end of the Phase in order of play with any other Deaths caused.

Examples:


 * You have a Death's Bite equipped and your enemy has a Haunted Creeper on the board. You play Perdition's Blade comboed targeting the Haunted Creeper. The Battlecry goes off first, reducing the Haunted Creeper to 0 Health. In the following Death Phase, either Deathrattle resolving first is decided by the order of play.
 * You have a Sword of Justice equipped and an Illidan Stormrage on the board, and play another Sword of Justice. During the On Play Phase, both weapons are regarded as being equipped, and we see the spawned Flame of Azzinoth get buffed twice. Similarly, if you replace a Cursed Blade with another Cursed Blade, Illidan causing your Knife Juggler to hit an enemy Axe Flinger, your hero will take 8 damage.
 * You have a Sword of Justice equipped and play a Jade Claws. The spawned Jade Golem will get the +1/+1 buff. Similarly, if you replace a Cursed Blade with a Perdition's Blade, targeting your hero, your hero will take twice damage from its Battlecry.

Playing a Hero card
When you play a Hero card, the following Sequence takes place:


 * 1) The card is removed from your hand and its Mana cost is paid.
 * 2) On Play Phase: All triggers on playing a card Queue and resolve here, such as Questing Adventurer, Fel Reaver and Illidan Stormrage.
 * 3) Battlecry Phase: First your hero is replaced by a Hero with the same current Health and maximum Health and gain Armor displayed on the card. Then replace your Hero Power with Hero’s Hero Power. Finally the Battlecry/Choose One is resolved.
 * 4) Hearthstone checks for win/loss/draw.

Whenever you replace your hero with another Hero, in general, everything that is an attribute of or an enchantment on your previous hero is gone, and the following things happen:
 * You are unfrozen.
 * All temporary enchantments are NOT destroyed (such as temporary Attack or Shadowblade's temporary Immune enchantment).
 * If the replacement hero does not have a new weapon, you keep your weapon. Else a new weapon is automatically equipped, destroying any previous weapon.
 * Your weapon swing is not refreshed.
 * Your Hero Power is replaced with the Hero card’s associated Hero Power, and is immediately usable.
 * Your hero becomes the class of the Hero card.

Playing/summoning a minion
When you Play a minion, the following Sequence takes place, which ends early if the minion leaves play (such as due to death):


 * 1) The card is removed from your hand and its Mana cost is paid. The card enters Play as a minion, creating a Summon Event and becoming interactible. If it targets, the target is remembered (and its validity is not checked again).
 * 2) On Play Phase: Hobgoblin, Questing Adventurer , Fel Reaver, Unbound Elemental, Tunnel Trogg , Illidan Stormrage and Crowd Favorite Queue and resolve here.
 * 3) (Because of the Summon Resolution Step, Starving Buzzard, One-eyed Cheat , Undertaker and more Queue and resolve for the played minion here.  )
 * 4) Battlecry Phase: First Mayor Noggenfogger resolves. Then the Battlecry/Combo/Choose One is fully resolved here.   (If Brann Bronzebeard was under your control when the Phase began, run Aura Update (Health/Attack) then resolve the Battlecry again.)
 * 5) After Play & After Summon Phase: First Mirror Entity, Repentance , Snipe , Sacred Trial    , Potion of Polymorph and Rumbling Elemental Queue and resolve. Then Ship's Cannon , Knife Juggler, and Sword of Justice  Queue and resolve. Note that after Patch 9.2.0.21517 these triggers can only work if they're valid when the Sequence starts.
 * 6) Hearthstone checks for win/loss/draw.

If a minion is merely summoned rather than played, it is inside of a larger Phase, so we are currently not processing Deaths or checking for win/loss/draw. The Sequence is now far simpler:


 * 1) The card is generated (or moved from your hand/deck if due to a Force Play mechanic) and enters Play, creating a Summon Event and becoming interactible.
 * 2) After Summon Phase

Notes:


 * Whenever an outermost Phase with a summon inside of it ends, the "Summon Resolution Step" occurs after the first Aura Update (Health/Attack) but before Death Creation Step, triggering on Summon Events that were made the previous Phase. (For more information, see the Summon Resolution Step section.)
 * The Battlecry's condition is only required to be valid when the minion is played, not when the Battlecry Phase begins, similar to the way it works for spells with target conditions. Mayor Noggenfogger only chooses the target that is valid at his timing.
 * The Battlecry still occurs even if the played minion Dies first. If the Battlecry uses the played minion as a target, then it affects its position in the Graveyard, not the position it had on the board, because it has already left play. This is probably a bug.
 * Note that if the played minion is stolen before the After Play Phase, an enemy Mirror Entity will no longer trigger. It is currently untested, but possible that enemy Knife Jugglers/Sword of Justice will trigger if the played minion is stolen before the After Summon Phase.
 * Interestingly, if the played minion leaves play during this Sequence, then enters play again (this is possible using Dread Infernal, Anub'ar Ambusher and Voidcaller), the minion being re-summoned will run triggers like Knife Juggler, and the minion being originally played will continue to resolve as though it never left play. So it is less correct to say 'the Sequence ends early' and more correct to say 'in general, triggers in this Sequence only trigger if the played minion is still in play and under your control'
 * Mirror Entity, Snipe, Repentance, Potion of Polymorph and Sacred Trial ignore mortally wounded/pending destroy minions. Hidden Cache and Frozen Clone trigger on mortally wounded/pending destroy minions. None of these Secrets trigger if the played minion has left play prior to the After Play Phase.
 * Lord Jaraxxus is an exception to the normal Sequence of playing a minion. When he replaces himself with your hero, he is actually removing (silently, as though hit by a Transform effect) Jaraxxus the Minion and creating Jaraxxus the Hero. This means that the After Summon Phase does not occur.

Examples:


 * You play Knife Juggler then Dr. Boom. When Dr. Boom's Battlecry (a Phase) begins,Boom Bots are summoned, and each one triggers the Knife Juggler to throw knives at enemy minions with Deathrattles. Even though minion summoning is a Sequence of multiple Phases, we are already inside of a Phase, so the entire Battlecry remains inside of one Phase, rather than starting and stopping. Finally when the Battlecry resolves, Deaths are processed and the Deathrattles go off.
 * Your opponent plays an Explosive Sheep, Snipe and Mirror Entity. You have a Sword of Justice, Knife Juggler (buffed to 3/4) and play an Elven Archer targetting the Explosive Sheep. The Elven Archer Dies as a result of the Battlecry Phase, and no further Phases are considered, so the enemy Snipe, Knife Juggler and Sword of Justice do not go off. (Prior to Patch 7.1, Mirror Entity then triggers and create a fresh, 1/1 Elven Archer. After Patch 7.1, it will not trigger.)
 * You have a Hobgoblin and Dire Wolf Alpha and play an Argent Squire next to the Dire Wolf Alpha. Because the newly played minion does not receive auras until after the Hobgoblin triggers, it gets its +2/+2 buff. If you hypothetically had an Illidan Stromrage (played before Hobgoblin), it will summon a Flame of Azzinoth causing Aura Update. So the original minion cannot get buff.
 * You equip a Sword of Justice and play a Bloodsail Raider, triggering your enemy's Mirror Entity. The mirrored copy, being Summoned after the Battlecry Phase but before the After Summon Phase (in which Sword of Justice triggers), remains a 3/3, then only yours becomes a 4/4.
 * You play Illidan Stormrage then a Knife Juggler. Illidan Stormrage triggers before Battlecries and before the usual, late phase Knife Juggler triggers on, summoning a Flame of Azzinoth. During THAT summon, the newly played Knife Juggler, being in play, is eligible to be Queued and trigger, throwing a knife for it.
 * If a card is added to your hand (going from 9 cards to 10 cards) between a Twilight Drake being played and its Battlecry going off, the Battlecry includes the new hand size (it gains 10 health, becoming 4/11).

Minions removed from play during summoning
A few effects can cause minions to be removed from play after a minion enters play but before its summoning completes, usually by mortally wounding them.

If the minion being played or the target of its Battlecry is removed, the Battlecry is not canceled, but uses the minion's new position and attributes in the Graveyard instead of its old in play status. Note that when minions are placed in the Graveyard, they are restored to default attributes, including their original maximum Health.

If the minion being played is removed from play before the After Play Phase, as of Patch 7.1, no Secrets will trigger on the played minion.

Examples:

Note: Illidan Stormrage is currently the only card that adds or removes minions from the board in between a minion's being played and its Battlecry, so it is used in conjunction with Knife Jugglers and minions that react to damage or death (e.g. Explosive Sheep and Abomination) to accomplish minion removal in most examples.


 * If a Twilight Drake becomes mortally wounded before the Battlecry Phase, it is removed from play before the Battlecry Phase can save it from dying (and most triggers in the summoning sequence will not work).
 * Faceless Manipulator and Druid of the Claw will still transform even if they are removed from play by the Illidan combo. (Before Patch 7.1, Mirror Entity would copy the post-transformed state from the Graveyard. ) However, if the post-transformed minion has a Deathrattle, it will not trigger, because the minion already died before the transformation happened.
 * If an Ironbeak Owl is removed from play before the Battlecry Phase, the silence still goes off on its target.
 * If Vol'jin targets a minion that is removed from play before the Battlecry Phase, the Health swap still goes off - and since minions moved to the Graveyard are reset to default attributes, Vol'jin gets full, undamaged Health instead of 0 Health. Conversely, if Vol'jin is removed from play before the Battlecry Phase, the target has its Health swapped with 2.
 * If a Defender of Argus is removed from play before the Battlecry Phase, it does not Taunt adjacent minions because the Battlecry triggered in the Graveyard.
 * If a C'Thun is removed from play before the Battlecry Phase, it will shoot 6 missiles, since his default state will be that of a 6/6 in the Graveyard.

Sequence of self-transform minions and Potion of Polymorph
If the minion you play transforms through battlecry (such as Faceless Manipulator or Druid of the Claw), its Battlecry Phase and After Play Phase will be different from normal minions:


 * 1) Battlecry Phase: First transform the original minion, then an After Play & After Summon Phase is inserted for the post-transform minion called Inserted Phase.
 * 2) After Play Phase: After Play triggers for the pre-transform minion are resolved.

Inserted Phase also starts for the Sheep when the minion you played is transformed by Potion of Polymorph in After Play & After Summon Phase or Inserted Phase.

Notes:


 * Similar to normal sequences, steps between phases also exist between the Battlecry Phase and After Play Phase above. You are considered to have summoned the post-transform minion. But you are not considered to have summoned the Sheep if it is polymorphed.
 * Some After Play triggers don't work in Inserted Phase, including Hidden Cache, Rumbling Elemental, Sherazin, Seed, Patches the Pirate, The Marsh Queen, The Caverns Below, Lesser Ruby Spellstone and Voidform's refreshing effect. Also, they don't require the original subject still present when they work in After Play Phase.
 * All After Summon triggers work in Inserted Phase. After Summon Phase doesn't exist for the original subject has been removed.
 * Some After Play triggers may have triggered before Potion of Polymorph, but they still work in Inserted Phase, including Swamp King Dred, Animated Berserker and Ixlid, Fungal Lord. This might be a bug.

Examples:


 * You Faceless Manipulator a Fire Fly. Your The Marsh Queen doesn't trigger unless the Faceless Manipulator is 1-cost, and your Lesser Ruby Spellstone doesn't get progress for upgradeing.
 * Similarly, you play Rogue Quest and then Faceless Manipulator a pirate. Your Quest is [Faceless Manipulator, 1/5] and Patches the Pirate isn't summoned from your deck.
 * You Faceless Manipulator a friendly Rumbling Elemental. Both Rumbling Elementals trigger for Faceless Manipulator.
 * You play a pirate and it's Potion of Polymorphed, your Ship's Cannon doesn't shoot.
 * You play Swamp King Dred then Potion of Polymorph. Your opponent plays Ysera. Ysera is first attacked by Dred, then polymorphed. The Sheep is also attacked by Dred.

Combat
When you order a minion to attack another minion, the following Sequence takes place: (As with other Sequences, if the attacker or defender leaves play for any reason, the current Phase will finish resolving but the Sequence will end early afterwards.)


 * 1) If you have Gladiator's Longbow or Candleshot at the start of Combat Sequence, you are Immune in the whole Sequence.
 * 2) Combat Preparation Phase: A Proposed Attack Event is resolved. If the defender changes, another Proposed Attack Event is created and placed in this Phase's Event Queue after the current Proposed Attack Event. (It will begin to resolve when the current Proposed Attack Event finishes resolving.) Finally, an Attack Event is resolved. Additionally, the attacker will lose Stealth.
 * 3) Hearthstone checks for win/loss/draw.
 * 4) Combat Phase: Damage is dealt simultaneously in the order (attack, counterattack) and resolved. The attacker's weapon loses durability (unless prevented due to the weapon being Immune). An After Attack Event is resolved even if 0 damage was dealt to the defender. Note that after Patch 9.2.0.21517 after attack triggers can only work if they're valid when the Sequence starts.
 * 5) Hearthstone checks for win/loss/draw.

The subjects of Combat are the attacker and defender. Even if the attacker or defender (or both) is mortally wounded or leaves play, triggers that ask what the current attacker/defender is will continue to be able to queue and resolve (assuming their other conditions are satisfied.)

Proposed Attack Event
Triggers on the Proposed Attack Event include those that can change the defender, cause the attacker to become mortally wounded or leave play, and so on.

At the start of resolving a Proposed Attack Event, triggers queue based on the defender at that moment, and will remain in the queue even if the defender changes.

When the defender changes, a new Proposed Attack Event is inserted into the Combat Preparation Phase's Event Queue after the currently resolving one. (It will therefore resolve once the current Proposed Attack Event finishes resolving, and therefore use the defender at that point in time.)

(As a reminder: Queuing conditions are only required to be true when the Event they trigger on starts to resolve, whereas trigger conditions are only required to be true when the trigger resolves.)

A full list is as follows:


 * Freezing Trap has a queuing condition of 'attacker is an enemy minion' and a trigger condition of 'attacker is not mortally wounded/pending destroy'.
 * Misdirection has a queuing condition of 'defender is your hero and there is a third, not mortally wounded, not Immune Character in play' and a trigger condition of 'attacker is in play and - if it is a minion - not mortally wounded, and there is a third, not mortally wounded, not Immune Character in play'.
 * Explosive Trap has a queuing condition of 'defender is your hero'.
 * Snake Trap has a queuing condition of 'defender is a friendly minion' and a trigger condition of 'board is not full'.
 * Noble Sacrifice has a trigger condition of 'board is not full'.
 * Vaporize has a queuing condition of 'attacker is an enemy minion and defender is your hero' and a trigger condition of 'attacker is in play and not mortally wounded'.
 * Ice Barrier has a condition of 'defender is your hero'.
 * Clumsy and Mogor the Ogre cannot trigger on a later Proposed Attack Event if they fail the 50% chance.
 * Clumsy has a queuing condition of 'attacker is this minion'.
 * Mogor the Ogre has a queuing condition of 'attacker is a minion'.
 * Shaku, the Collector has a queuing condition of 'attacker is this minion'.
 * Mayor Noggenfogger has a condition of 'attacker is still on the battlefield'. He could choose any enemy as the new target.
 * Genzo, the Shark has a queuing condition of 'attacker is this minion'. Additionally, it currently has a bug (like the old Cutpurse bug ) that lets it trigger twice if its target is changed after triggering once.
 * Gladiator's Longbow has a queuing condition of 'attacker is your hero'. (This means that Gladiator's Longbow vs Explosive Trap is determined by the Dominant Player Bug.)
 * Sudden Betrayal has a condition of 'defender is your hero, and there is a not mortally wounded, not Immune minion near the attacker'.
 * Wandering Monster has a condition of 'defender is your hero, and your board is not full'.

Attack Event
Triggers on the Attack Event include those that need to occur only once the final defender is known, or those that do not significantly affect the game state. The Attack Event is only resolved if the previous Proposed Attack Event did not change the defender. A full list is as follows:


 * Truesilver Champion has a condition of 'attacker is your hero'.
 * Gorehowl has a condition of 'attacker is your hero and defender is a minion'. It attaches an Enchantment called "Bloodrage" to Gorehowl, which makes Gorehowl Immune and triggers on the After Attack Event.
 * Cutpurse has a condition of 'attacker is this minion and defender is a hero'. It implicitly requires the Cutpurse to still be in play.
 * Power Word: Glory has a condition of 'attacker is this minion'. It implicitly requires the attacker to still be in play, as it gets detached when the attacker leaves play.
 * Blessing of Wisdom has a condition of 'attacker is this minion'. It implicitly requires the attacker to still be in play, as it gets detached when the attacker leaves play.

After Attack Event
An After Attack Event is resolved as long as the attack was successful, even if it dealt 0 damage.

(Note that unlike other triggers that go 'after' something, such as Rumbling Elemental and Djinni of Zephyrs, the After Attack Event is resolved in the same Phase, not a later Phase, as the combat damage, meaning death processing is not done in-between.)

Triggers on the After Attack Event are as follows:


 * Gorehowl has a condition of 'attacker is your hero and defender is a minion' and attaches to itself an Enchantment granting -1 Attack.
 * Gorehowl's Enchantment "Bloodrage" has a condition of 'attacker is your hero' and triggers to detach, ending Gorehowl's temporary Immune state.
 * Bear Trap has a condition of 'defender is your hero and board is not full'.
 * Foe Reaper 4000/Magnataur Alpha has a condition of 'attacker is this minion'.

Examples
Proposed Attack Events/Attack Events


 * Because every Proposed Attack Event resolves before the Attack Event, some triggers on attacking will always trigger before others regardless of order of play. For example, Explosive Trap always triggers before Truesilver Champion, and Freezing Trap always triggers before Blessing of Wisdom.
 * Because Proposed Attack Events are created and resolved until the proposed defender does not change, triggers that change the proposed defender like Clumsy, Mogor the Ogre and Noble Sacrifice can allow Secrets related to attacking an enemy Hero AND attacking an enemy Minion to trigger on the same attack:
 * If you have an Ogre Brute and your opponent (the Dominant Player) has an Explosive Trap, you attack a minion with the Ogre Brute but Clumsy triggers and targets the enemy Hero, the Explosive Trap goes off.
 * Conversely, since triggers on a Proposed Attack Event remain queued for the original proposed defender if it changes, you can't prevent an enemy Secret from triggering by redirecting away from it.
 * If an Ogre Brute is played (by the Dominant Player) and your opponent has an Explosive Trap, the Ogre Brute attacks the enemy Hero but Clumsy triggers first, the Explosive Trap still goes off. Similarly, Misdirection and Noble Sacrifice, regardless of order of play, both go off when your hero is attacked:
 * However, if you redirect onto an enemy target and redirect off of it while still resolving the same Proposed Attack Event, then since no Proposed Attack Event ever started being resolved with that specific target, Secrets related to that target being the defender will not trigger!
 * If you attack with an Ogre Brute into an enemy minion, and the first Proposed Attack Event queues and resolves Clumsy (targeting the enemy Hero) then Noble Sacrifice (targeting an enemy minion), the second Proposed Attack Event now queues and resolves with the enemy minion as the defender. Despite briefly attacking the enemy Hero, Explosive Trap will not trigger.
 * Many Secrets related to combat have a trigger condition that prevents them from triggering and doing 'nothing' (like Freezing Trap doesn't trigger if the attacker is mortally wounded by Explosive Trap first, and Noble Sacrifice doesn't trigger if there's no room). However, not all such trigger conditions exist - for example, Explosive Trap triggers even if the attacker is no longer in play, and Noble Sacrifice triggers even if the attacker is no longer in play or mortally wounded.
 * Unlike Proposed Attack Event triggers, Attack Event triggers will only run if the final attack satisfies their condition.
 * If an Ogre Brute targets the enemy Hero but Clumsy triggers and redirects it to target an enemy minion, regardless of order of play, the enemy Ice Barrier never triggers.

Death processing


 * As with all other Sequences in Hearthstone, death processing is not done in the middle of a Phase, but is done between Phases, and Death Phases inserted to resolve triggers on Death Events until no new deaths occur.

Examples:


 * It is commonly said that Truesilver Champion heals you before Explosive Trap, and that's why you stay alive. This is not true - you actually stay alive because your hero cannot die in the middle of a Phase (which the Preparation Phase is), and that is also why the order of play does not matter. (Similar interactions, such as Floating Watcher vs Explosive Trap, work the same way.)

Auras


 * As with all other Sequences, Auras added or removed after the Combat Preparation Phase will affect the outcome of the Combat Phase, such as changing Attack values or adding/removing Immune status.

Ending the Game


 * Normally, Sequences wait to be fully resolved before checking for win/loss/draw. However, the Combat sequence additionally checks just before the Combat Phase would begin. This can cause what 'should be a draw' to be a loss instead, usually due to Explosive Trap.
 * The visual result is that the attacking character remains suspended in mid-air as the game ends.
 * A combat started by Swamp King Dred's effect also has Combat Preparation Phase, but no Death Creation Step or check for win/loss/draw run after it.

Examples:


 * If you are at 2 Health and your opponent at 2 Health and attack with Stormwind Knight into Explosive Trap, the Explosive Trap triggers, and Hearthstone checks for win/loss/draw. The Stormwind Knight's attack never finishes, and you lose.
 * If you have an Auchenai Soulpriest on the field, are at 4 Health and attack with a minion which you previously cast Power Word: Glory on, the Power Word Glory triggers in the Combat Preparation Phase, mortally wounding your Hero. Win/loss/draw is checked before the Combat Phase, and you lose the game, even if the attack finishing would have caused a draw.
 * If you are at 2 Health and your opponent at 2 Health and attack with Stormwind Knight into Explosive Trap and Freezing Trap (played in that order), the Explosive Trap triggers, mortally wounding your hero, then the Freezing Trap triggers, sending the Stormwind Knight back into your hand, then Hearthstone checks for win/loss/draw, and you lose. (You of course still lose if the order is the other way around, as Explosive Trap will trigger anyway.)
 * As usual, Hearthstone checks (again) for win/loss/draw when the Sequence is fully resolved. For example: You have a Knife Juggler and Bear Trap in play and your opponent's Health is 1. Your opponent attacks your Hero with a minion, reducing you to 0 or less Health, but before the game ends, your Bear Trap triggers, triggering the Knife Juggler to reduce your opponent's Health to 0. Then, the game ends in a draw

Ordering of damage in the Combat Phase


 * Because the weapon losing durability and the damage are in the same Phase, weapons with Deathrattles such as Death's Bite have their Deaths Events considered in order of play with the minion that died, in the following Death Phase.
 * If both minions trigger when they take damage (such as a Grim Patron and an Imp Gang Boss), the defender ALWAYS triggers first, regardless of order of play. Keep in mind that Grim Patron has a trigger condition of 'not mortally wounded', so even if it survived the initial damaged, follow-up damage may prevent Grim Patron from triggering.
 * If both minions trigger when they deal damage (such as Queen of Pain and Poison), the attacker ALWAYS triggers first, regardless of order of play.

Examples:


 * You play a Grim Patron. Your opponent has a Knife Juggler and plays an Imp Gang Boss (the knife hits face). On your turn, your Grim Patron attacks their Imp Gang Boss. The simultaneous damage triggers are queued in the order [Imp Gang Boss, Grim Patron] because the defender queues first. An Imp is summoned, triggering the allied Knife Juggler to throw a knife and mortally wound your Grim Patron. Now your Grim Patron would trigger, but it is mortally wounded, so the trigger condition fails and you do not get a new Grim Patron.
 * You attack with a 4/1 Death's Bite into a 3/4 Sludge Belcher, mortally wounding both the weapon and the minion. Whether the Slime appears first (and thus becomes a 1/1) or second (and thus stays a 1/2) depends on whether the minion or weapon entered play first.

Unusual attackers/defenders


 * Besides the attacker or defender leaving play, there are no other known conditions that will cause the Combat Phase to be skipped - for example, the defender becoming an ally, the attacker becoming an enemy, the attacking character becoming 0 Attack and the attacking weapon being replaced with a new weapon all allow Combat Phase to proceed.

Examples:


 * You attack with a Truesilver Champion into a Novice Engineer. During the Preparation Phase, an allied Shadowboxer triggers and mortally wounds the Novice Engineer. By the time the Combat Phase is reached, the Novice Engineer has been killed and removed from play, so no combat occurs, and you can attack again.
 * You have a 5/1 Sylvanas Windrunner and attack with a Truesilver Champion into an enemy Shadowboxer. During the Preparation Phase, the enemy Shadowboxer triggers and mortally wounds your Sylvanas Windrunner. By the time the Combat Phase is reached, the Shadowboxer has been stolen to your side, but you still exchange damage with it and kill it.
 * If resolving the Preparation Phase caused your weapon to be replaced because Tirion Fordring's Deathrattle was triggered, you perform the attack with the newly equipped weapon.
 * If resolving the Preparation Phase caused your Gorehowl to have 0 Attack because an allied Spiteful Smith died and its Aura stopped, you perform the attack but deal 0 damage, and lose durability/become exhausted. This also works if the attacking minion becomes 0 Attack.
 * If resolving the Preparation Phase caused your attacker to become an enemy, it still performs its attack on its now-ally, and will perform it with Auras such as from an enemy Stormwind Champion.
 * If a friendly minion can only attack because it has temporary Charge from Tundra Rhino, the Tundra Rhino does not have to survive until the actual combat happens (for example, if it dies to Explosive Trap, the combat will not be cancelled).

Cancelling combat


 * If the attack is cancelled (after 0-1 Death Phases), the attacker has not used one of their attacks for this turn and can immediately attack again.
 * However, if combat is cancelled because the defender dies after 2 or more Death Phases, such as Noble Sacrifice triggering Knife Juggler mortally wounding a Boom Bot, which in the subsequent Death Phase mortally wounds the defender, which THEN dies, then the attack is cancelled AND the attacker cannot attack again this turn. We can tell this is a bug, because the minion also remains visually in the wrong place on the board.

Other


 * Before Patch 8.2.0.19506， due to the way Gorehowl is coded, if you propose to attack a minion, but the attack is cancelled due to the defender dying (an easy way is to be Misdirection redirected onto a minion, then the minion is mortally wounded by Explosive Trap), Gorehowl will continue to have "Bloodrage" attached and continue to be Immune. Enemy Bloodsail Corsairs will not deal damage (since Immune prevents damage), but it can still be destroyed. In addition, if you perform an attack with this Gorehowl on the enemy Hero, it will not lose Durability OR Attack, but will lose "Bloodrage" and thus its Immune state. Now "Bloodrage" will be removed if the battle is canceled.


 * Sometimes Combat is still cancelled when both attacker and defender are alive. For example, you attack with your 6/2 self buffed Floating Watcher into enemy Explosive Trap. Watcher cannot finish the attack but is still alive as a 8/2, and it cannot attack again. If it is an unbuffed 4/2 previously, it attacks successfully.
 * Before Patch 5.2.0.13714 (2016-07-14), Ice Barrier was an Attack Event trigger rather than a Proposed Attack Event trigger.

Using your Hero Power
Related Video for this section: [Hearthstone Science TGT Science #01: Inspire and Advanced Mechanics]

The Hero Power Sequence is as follows:


 * Hero Power Phase: Your Hero Power takes effect then is exhausted. (The "number of times you have used your Hero Power this turn" and "number of times you have used your Hero Power this game" counters are increased by 1.)
 * Inspire Phase: Inspire triggers, Poisoned Blade, Dart Trap and Ice Walker Queue and Resolve here. Note that after Patch 9.2.0.21517 these triggers can only work if they're valid when the Sequence starts.
 * Hearthstone checks for win/loss/draw.

Notes
 * Inspire also belongs to 'After ...' effects. After Patch9.2.0.21517 it can only work if it's valid at an earlier timing.
 * Ice Walker still triggers even the target is not present, including dying, being removed out by Transmute Spirit and being returned to hand by Coliseum Manager. Moorabi can get a copy of it. Multiple Ice Walker can trigger Moorabi multiple times.

Examples:
 * You use your Hero Power to kill an enemy Deathlord, putting into play for you an Inspire minion. Its Inspire effect cannot work.
 * If your Hero dies as a result of your Hero Power or deaths caused by it, a friendly Tournament Medic will not be able to heal you because of the Death Creation Step between Phases. However, if you play a Spawn of Shadows and a Tournament Medic in that order, the Spawn of Shadows can mortally wound you, then the Tournament Medic can heal you back to positive Health, because the two triggers are in the same Phase.
 * If you use your Hero Power to kill the enemy Hero, then a Spawn of Shadows triggers in the Inspire Phase and reduces you to 0 Health, then the game ends in a tie instead of a win, because Hearthstone checks for win/loss/draw only at the end of the Sequence.
 * If you play Brave Archer, Recruiter and a second Brave Archer, then use your Hero Power with an empty hand, the first Brave Archer triggers, then the Recruiter triggers, then the second Brave Archer does not trigger, because it checks its condition when triggering and decides not to trigger.
 * If you use your Hero Power to kill an enemy Mal'Ganis, then a Spawn of Shadows triggers in the Inspire Phase, the enemy Hero will take 4 damage because Aura Update (Other) runs between Phases.

Refreshing your Hero Power
TODO: Re-test Garrison Commander entering play and being bounced/stolen immediately (using Deathlord + Anub'ar Ambusher/Sylvanas Windrunner) to 100% confirm it's Aura Update (Health/Attack) timing.

Your Hero Power is refreshed (and thus made usable again) at the following timings:

Notes:
 * At the beginning of your turn, when the "number of times you have used your Hero Power this turn" counter is reset too;
 * When you replace your Hero Power with a new one (casting spells like Shadowform, or replacing your hero using Lord Jaraxxus or Majordomo Executus), even if it's with the exact same one; (Replacing your Hero Power also resets the "number of times you have used your Hero Power this turn" counter.)
 * At Aura Update (Health/Attack) timing, if you control a Coldarra Drake;
 * At Aura Update (Health/Attack) timing, if you control a Garrison Commander and the "number of times you have used your Hero Power this turn" counter is 1;
 * When you cast a spell to activate Auctionmaster Beardo;
 * When you play a card to activate Voidform;
 * When you activate the battlecry of Blackwald Pixie.
 * As of Patch 5.0.0.12574 (WotOG patch), Coldarra Drake and Garrison Commander refresh your Hero Power at Aura Update (Health/Attack) timing as long as you control them, regardless of how you began to control them (including stealing them and transforming into them). They do not unrefresh your Hero Power if they leave your control (such as due to death).
 * Coldarra Drake and Garrison Commander used to be a combination of a Summon Resolution Step trigger (for when they were initally played, summoned or transformed into by a Battlecry) and an Inspire trigger (for after you use your Hero Power thereafter). This caused some bugs, such as Mind Controlling a Garrison Commander not refreshing your Hero Power.

Examples:
 * You use your Hero Power once then Mind Control a Garrison Commander. Your Hero Power is refreshed.
 * You use your Hero Power once then Faceless Manipulator an enemy Garrison Commander. Your Hero Power is refreshed.
 * You use your Hero Power to kill your Garrison Commander. Your Hero Power is refreshed, then the minion dies.
 * Since when you replace your Hero Power the "number of times you have used your Hero Power this turn" counter is reset to 0, Garrison Commander will allow you 2 more uses of your new Hero Power that turn.

Replacing your hero
Whenever you replace your hero with a new one, in general, everything that is an attribute of or an enchantment on your previous hero is gone, and the following things happen:
 * Damage and Armor are reset to 0.
 * You are unfrozen.
 * All temporary enchantments are destroyed (such as Ice Block's temporary Immune enchantment).
 * If the replacement hero is Ragnaros, you keep your weapon. If it is Lord Jaraxxus, a new weapon is automatically equipped, destroying any previous weapon.
 * Your weapon swing is not refreshed.
 * Your Hero Power is replaced with the replacement hero's, and is immediately usable again.
 * Your hero becomes the type of whatever replaced it. For example, if your hero is Lord Jaraxxus, you are targetable as a Demon.
 * Your hero becomes the class of whatever replaced it for the purposes of Nefarian, Discover, Burgle etc. (Lord Jaraxxus the Hero is Warlock. Ragnaros is Neutral and each such effect has a fallback. For example, Nefarian gives two Tail Swipes and Burgle gives two coins. )

Losing the game
If/when Hearthstone runs the Death Creation Step, your current Hero is mortally wounded or pending destroy, the next time Hearthstone checks for win/loss/death you will lose the game. (Technical details: When an in-play Hero dies, the PLAYSTATE tag on the corresponding Player Entity is set to LOSING.) You still lose the game even if your Hero is later replaced.

Note that if your Hero is replaced in the same phase that it is mortally wounded, this means you do not lose the game (for a similar reason why Truesilver Champion + Explosive Trap lets you avoid losing the game). Currently Majordomo Executus's Deathrattle is the only way to accomplish this:
 * For example, you are at 2 Health and have a 4/1 Abomination and 9/1 Majordomo Executus played in that order, and your enemy plays Arcane Explosion. Both your minions die, and a Death Phase queues both their Deathrattles - the Abomination's, which mortally wounds you, and Majordomo Executus's, which replaces your hero with Ragnaros. At the end of the Death Phase, Hearthstone checks for additional deaths, and since your hero is not mortally wounded at this point, you do not lose the game.
 * Consider instead, you are at 2 Health and have a 9/2 Majordomo Executus when your enemy plays Hellfire, mortally wounding you in the Spell Text Phase. That phase ends, and Hearthstone checks for deaths, discovering both you and Majordomo Executus are dead, so a Death Phase begins. The Deathrattle will replace you with Ragnaros, but it is too late, since Hearthstone already considers you dead. Once the Death Phase is over, the game ends in your loss.

Also note that killing a Hero that is no longer in-play does not result in the game ending: Alexstrasza can raise the maximum Health of the Ragnaros hero from 8 to 15. It is a permanent increase.
 * For example, if you cast Sacrificial Pact on the enemy Lord Jaraxxus hero, but Violet Teacher plus Knife Juggler kills an enemy Majordomo Executus, replacing the enemy hero with Ragnaros before the Spell Text Phase begins, Sacrificial Pact will target and destroy Lord Jaraxxus the Hero in the Setaside Zone. No visible side-effects occur, and the game continues.

Transformation
When a minion is transformed, it is removed from play immediately and replaced by the minion it got transformed into. All enchantments, triggers, Deathrattles, etc. are detached. This does not count as dying for the purposes of on-Death triggers and Secrets and Resurrect/Kel'Thuzad, nor does it count as summoning for the purposes of on-summon triggers. When the outermost Phase ends or a new minion is summoned, it stops emitting any auras it had.

If you play a self-transform minion (such as Faceless Manipulator), new After Play Phase and After Summon Phase are inserted to guarantee further triggers to run. Similarly, if your played minion is transformed by Potion of Polymorph, later triggers work on the Sheep. For more information, see the Sequence of self-transform minions and Potion of Polymorph section.

Besides, minions resulting from non-spell transformations are counted as 'summoning a minion' and allowed to participate in the Summon Resolution Step (see the Summon Resolution Step section).

Examples:


 * Your enemy has Bolvar Fordragon in their hand and a Bloodfen Raptor, Cult Master, Starving Buzzard, Knife Juggler, Kel'Thuzad in play. You cast Polymorph on the Bloodfen Raptor and end your turn. Nothing triggers.
 * You have a Starving Buzzard and play a Druid of the Fang. The Starving Buzzard does not trigger at its usual timing, but instead at the end of the inserted phases during the Summon Resolution Step.
 * You have a Sword of Justice and your enemy has a Boulderfist Ogre. You play a Faceless Manipulator targetting the Boulderfist Ogre. The Sword of Justice triggers in a later Phase than the Battlecry Phase, so it gives the newly transformed Boulderfist Ogre +1/+1, not the Faceless Manipulator.
 * Your opponent plays a Boulderfist Ogre and Mirror Entity. You play a Faceless Manipulator targeting the Boulderfist Ogre. The Mirror Entity triggers in a later Phase than the Battlecry Phase, so it sees a Boulderfist Ogre being summoned and makes a copy of it.
 * You have 7 minions and play Thrall, Deathseer. One of your minions is transformed into an Starving Buzzard and another is transformed into a beast. You draw a card for it. However, if these minions are transformed through Evolve, you will not draw a card.

Exceptions:


 * Shifter Zerus does not work like usual transformation effects. Every time he transforms in your hand, he is still the same Entity but has changed his Card ID, and all attached Enchantments remain attached. In addition, he tracks that he should keep changing by attaching the Enchantment 'Shifting' (OG_123e) to himself. This Enchantment is detached if Shifter Zerus enters play, and copies of cards in hand do not copy attached Enchantments, so cards like Mind Vision will copy only what minion Shifter Zerus is, and the copy will not keep changing.

Copy effects
Effects that create a card in your hand that is a copy of another card (such as Mind Vision, Chromaggus, Thoughtsteal and Convert) do not copy attached Enchantments, such as those that affect Health/Attack (such as from The Mistcaller) or those that affect Mana Cost (such as from Far Sight or Emperor Thaurissan).

Effects that put a minion into play that's a copy of another minion in play (such as Echoing Ooze, Mirror Entity, Faceless Manipulator) copy all of the minion's state and all attached Enchantments, with a few exceptions:
 * Auras affecting the target minion aren't copied. For example, if you copy a minion that is at 1 current Health due to an allied Stormwind Champion with Faceless Manipulator, your copy will have 0 current Health and immediately die.
 * Obviously, controller, zone position, zone, etc. are not copied and are overridden by the act of creating the copy.
 * Similarly, how long the original minion has been in play is not copied, meaning the copy will have summoning sickness (if not overridden by Charge).

Health
Rule H1: Any time a minion's maximum Health is increased, its current Health is increased by the same amount. Rule H2: However, when a minion's maximum Health is reduced, its current Health is only reduced if it exceeds the new maximum.


 * Minions track both a "current Health" and a "maximum Health" stat.
 * A 1/1 minion gaining +1 Health becomes a 1/2. There is no distinction between a minion's 'natural' Health and Health granted through auras/enchantments.
 * Effects which grant a minion +X Health actually work by increasing the minion's maximum Health; their current is automatically increased by the same amount.
 * Losing current Health due to a reduced maximum Health does not count as damage, in the same way gaining Health does not count as healing.
 * Silencing off a maximum Health reduction is equivalent to adding a maximum Health enchantment of the same value, and vice versa.

Examples


 * An Injured Blademaster with 3 current Health out of 7 maximum may be increased to 4 Health (and 8 maximum) by a friendly Stormwind Champion. If the Champion is then silenced, the Injured Blademaster's maximum Health is returned to 7, but his current Health of 4 will not be reduced back down, since it does not exceed the maximum.
 * A Chillwind Yeti (4/5 with max 5 Health) is played. Crazed Alchemist gets played on it and it (becomes 5/4 with max 4 Health). 1 damage is done to it (becomes 5/3 with max 4 Health). When it then gets silenced, the Yeti becomes 4/4 with max 5 Health. This is because its maximum Health is increased from 4 to 5 by the Silence effect, so this also causes the current Health to go up from 3 to 4.
 * An Injured Blademaster is 4/3 with a maximum Health of 7. When you cast Divine Spirit on it, the spell increases both the current and maximum health of the Blademaster by 3 (the value of its current Health at the time of resolving the spell). This resulting Blademaster is a 4/6 with a maximum Health of 10.

Exceptions


 * Crazed Alchemist and Reversing Switch do not raise or decrease the maximum Health stat. They apply a buff that sets a new maximum Health (see Enchantments section). At the time of application, it also sets the current Health to the new maximum Health.

Enchantments
Rule E1: If a minion has multiple enchantments, they are applied to the minion in order of play.


 * This is the same order shown when mousing over the minion - oldest to newest, top to bottom. However, that order does not always show repeated applications of the same enchantment.

Examples:


 * You have a 6/9 Gahz'rilla and play Lance Carrier (buffing to 8/9) then target it with a Cruel Taskmaster. The damage and buff of Cruel Taskmaster are simultaneous, so Gahz'rilla triggers after being buffed to 10/8, doubling to 20/8. Finally, you target it with an Abusive Sergeant, buffing it to 22/8 (returning to 20/8 after your turn ends). If enchantments were applied in any other order, the resulting Attack value would be different.

Rule E2: When a temporary enchantment is removed from the middle of the enchantment list, the minion's state is recalculated from scratch.


 * This as opposed to, for example, a 'reverse of the enchantment' enchantment being added to the end of the list.

Examples:


 * If a 6/9 Gahz'rilla has its Attack temporarily reduced to 4 by a Shrinkmeister, and then suffers damage, the order of the enchantment stack will result in a total of 8 Attack: (((6 - 2) * 2) = 8). At the end of the turn, the Shrinkmeister's buff will be removed, resulting in the Gahz'rilla's Attack increasing not by 2, but by 4, to a total of 12: ((6 * 2) = 12). If enchantments were not dynamically recalculated, the Gahz'rilla's Attack would instead be increased to 10, since its previous net result of +4 Attack had already been established prior to the removal of the Shrinkmeister's buff.

Rule E3: When a minion is Enraged, it creates an enchantment with that effect. If it later becomes un-Enraged (losing the enchantment) and then re-Enraged, it creates a new enchantment, rather than re-creating the old one with its old order of play.

Examples:


 * You play an Amani Berserker and Enrage it, giving it 5 Attack. You then play Humility on it, giving it 1 Attack. You then heal and Enrage it a second time - the new Enrage is at the end of order of play, going after the Humility effect and it now has 4 Attack.

Notes and Exceptions:


 * Enchantments like Crazed Alchemist/Reversing Switch that swap the Attack and Health of a minion are calculated by directly setting the Attack and Health to those new values (as opposed to, for example, calculating how much to change Attack and Health by and making that enchantment), and thus temporary enchantments placed prior to the stat reversal ending will have no observable effect.
 * However, enchantments that double Attack like Blessed Champion and Gahz'rilla do not double auras, because the effect of the enchantment is to double the Attack prior to the enchantment, so when the aura is moved to the end of the list again it is not doubled.
 * Enrage Enchantments do not seem to apply their effect immediately, but instead do so at the next Aura Update (Health/Attack) Step.

Auras
Auras are ongoing effects tied to Entities which affect other Entities (such as cards, minions, your hero or itself) as long as the provider is in play (and not silenced). Every time Aura Update (Health/Attack) runs, Auras are processed strictly after all other Enchantments, even if the Aura was in place prior to the other buffs being gained. (Note that Enchantments take affect immediately when applied, and so will briefly apply 'out of order'.)

Let us review Rule 4:

Rule 4a: After the outermost Phase ends, Hearthstone does an Aura Update (Health/Attack), then does the Death Creation Step (Looks for all mortally wounded (0 or less Health)/pending destroy (hit with a destroy effect) Entities and kills them, removing them from play simultaneously), then does an Aura Update (Other). Entities that have been removed from play cannot trigger, be triggered, or emit auras, and do not take up space. Rule 4b: Besides, whenever a minion is summoned (but not played), Hearthstone updates both kinds of Auras. Rule 4c: Some Auras that are known to update in Aura Update (Other) is as follows: Baron Rivendare, Auchenai Soulpriest, Brann Bronzebeard, Mal'Ganis's Immune effect, Prophet Velen, Violet Illusionist, Drakkari Enchanter, The Four Horsemen (Hero Power). Rule 4d: Enchantments apply and modify Health/Attack/Mana costs the moment they are attached. However, during Aura Update (Health/Attack), the Enchantment List is re-processed and Health/Attack Auras, having a priority later than Health/Attack Enchantments, will be moved to the end of the Enchantment List during this timing. (However, Mana Cost Auras have no special priority compared to Mana Cost Enchantments.)


 * When a minion is played, its Aura is sent for the first time before the Battlecry Phase. When a minion is stolen, it does not start emitting its aura until the outermost Phase ends, unless a new minion is summoned.
 * Until the moment it is removed from play, the Entity can be brought back from 0 or less Health by healing or Health buffs, and still shares auras. This is important when multiple minions are attacked simultaneously, or when a hero dies in the same Sequence as minions with Deathrattles.
 * If you kill a minion with an aura and a minion with a Deathrattle simultaneously, non-Health effects of the aura are not active during the following Death Phase because the minion is removed from play. However, Health effects of the aura will be active, because Hearthstone does not recalculate Health changes after the minions are killed, unless a new minion is summoned.  However, a health-granting aura such as Mal'Ganis can save a minion from dying, even if it enters play the same Phase the other minion was mortally wounded, because the aura recalculation is done before the Death Creation Step.
 * Auras are not recalculated due to minions leaving play or due to minions being stolen in the middle of a Phase..
 * Brann Bronzebeard, Baron Rivendare and Drakkari Enchanter check before an Event starts. This means if one Battlecry/Deathrattle/End of turn effect summons them, it will not trigger again. But Deathrattles/End of turn effects that follow can benefit, for Aura (Other) is updated when you summon them.
 * Some auras in the game have a higher Priority than others. This means that order of play does not matter if one aura's Priority is simply higher. For example, Summoning Portal's aura always comes first (meaning also having a Mechwarper makes Harvest Golems cost 0 mana, regardless of play order) and Lightspawn's and 'Tar' minions' auras always come last.
 * Despite not visually updating, enchantments take effect the moment they are created.

Notes and Exceptions


 * There is one known exception to 'auras are applied strictly after all other enchantments' - Summoning Portal's Priority is so high it's applied before enchantments.
 * The interaction between Crazed Alchemist/Reversing Switch and auras is as follows: The newly created buff directly sets Attack and Health to the opposite values (e.g. as opposed to computing an Attack change and a Health change and creating that buff) considering all auras, and then the auras are re-applied afterwards at the next State update, creating the impression that the auras have been 'counted twice'.

Silence
If a minion is being given a Health increase by an Aura such as Stormwind Champion, then Silencing that minion will not temporarily remove the Aura's effect (which would then be added back at the next Aura Update (Health/Attack) Step).

A consequence of this effect is that if a 1/1 is buffed to 2/2 by Stormwind Champion then damaged for 1, if it is silenced, it does not temporarily become a 1/1, get buffed by Stormwind Champion again and thus become an undamaged 2/2.

However, besides not removing the effects of Auras, Silence seems to immediately remove all other properties of the minion it targets. For example, Earth Shocking a friendly Wrath of Air Totem will remove the Spell Damage +1 before the 1 damage is dealt, and thus you will deal only 1 damage, not 2.

Zones
Each Entity in a game of Hearthstone exists in one of several specific areas, called Zones. In addition, it has a 'controller', which determines which half of the zone it is. Changing controller will also be referred to as changing 'zones', even though it is technically different.

Note that cards, minions, weapons, heroes, etc are all Entities. Playing a minion card moves the Entity from the Hand Zone to the Play Zone, rather than destroying the card and creating the minion, for example.

The Zones are:


 * Visible
 * Play
 * Deck
 * Hand
 * Secret
 * Not fully visible
 * Graveyard
 * Removed from game
 * Set aside
 * Other
 * Invalid

Minions that are killed and removed from play have their attributes (most notably current Health) reset to a default state and are moved to the "Graveyard Zone". Spells after being cast, destroyed and equipped over weapons, dead heroes and discarded cards (from hand or from deck) also go to the "Graveyard Zone".

The "Set Aside Zone" holds cards and Entities existing in any intermediate or 'not really on the board' state, such as the three cards presented to you by Tracking, the original minion after Weasel Tunneler's Deathrattle (which shuffles a copy; Malorne's Deathrattle instead shuffles the original minion), the prior state of transformed minions and Lord Jaraxxus the minion after his Battlecry occurs. The Amazing Reno's Battlecry works by moving all minions to the Set Aside Zone.

The "Removed From Game Zone" holds enchantments that have expired, been detached or been silenced off.

Limits
Hearthstone imposes limitations on how many Entities can be in each Zone. The limitations are:


 * 5 Secrets (or Quest, or Sidequests) per player's "Secret Zone", one Quest at most and only one copy of a specific Secret or Sidequest per "Secret Zone"
 * 10 cards per player's hand
 * 7 minions, 1 hero, 1 weapon, 1 hero power per player's "Battlefield Zone"
 * 60 cards per player's deck

Rule Z0: If Hearthstone would generate a new Entity in a Zone but the limit has been reached, instead nothing happens.


 * Note that attempting to generate an Entity in a full zone does not generate and then destroy it. Rather, nothing happens.

Moving between Zones
''TODO: There seems to be some kind of new rule that says that a minion can't be bounced to deck and then from deck to hand. Or maybe it's not a moving between zones rule, but a rule about triggers' trigger conditions? Figure out which it is and edit the appropriate section of the two. See https://github.com/HearthSim/hs-bugs/issues/636 ''

Rule Z1: When an Entity tries to move from one Zone to another, it first checks if the destination is full. If it is, it instead dies and moves to the Graveyard Zone. Rule Z1b: If an Entity tries to move from a Zone to the Zone it's already in, do not apply Rule Z1 (such as steal effects on a minion you already control, or bounce effects on a minion already in your hand). However, other effects of the zone change still happen (such as gaining summoning sickness). Rule Z2: If multiple Entities are moved from one Zone to another simultaneously, they check and move themselves in order of play, and thus newest minions are the ones that get Destroyed if there is insufficient room.


 * This means that after the outermost Phase ends, its Death will be resolved in the subsequent Death Phase in order of play.
 * Note that if it was a minion, its Death Event is resolved in the Zone it was in, not the Zone it tried to go to. This is because the attempted Zone change did not happen.

Examples:


 * Your opponent plays a Piloted Shredder and Explosive Sheep. On your turn, he has 9 cards in his hand, and you play Vanish. First, the Piloted Shredder is bounced back, then the Explosive Sheep finds there is no room, so is destroyed. After the Spell Text Phase ends, a Death Phase begins where the Explosive Sheep's Deathrattle goes off.
 * You have 6 minions on your board and your opponent has 4. You play a Mind Control Tech. The stolen minion, a Mad Scientist has no room, and is destroyed. After the Battlecry Phase ends, a Death Phase begins where Mirror Entity is put into play. (As of Patch 4.3.0.12266 (2016-04-14), Cabal Shadow Priest can be used the same way. )

Exceptions:


 * Force play mechanics such as Deathlord and Ancestor's Call are different from steal/bounce mechanics - they do not destroy/discard the minion if there is no room in the destination zone. Instead, they do nothing. (Or in the case of Varian Wrynn, the minion is moved to your hand instead of force played.)
 * Likely due to a bug, effects that move a card to your deck, such as Entomb and Patch 4.0.0.10833-on Malorne do not respect the limit of 60 cards in the deck. (Mind Control effects moving a card from one deck to another also do not respect the limit.)
 * Due to a bug, if you steal a card from your opponent's hand (such as by targeting Mind Control on a minion bounced to the hand by Anub'ar Ambusher before the spell resolves), the limit of 10 cards in your hand is not checked.

Rule Z3: If Kezan Mystic tries to steal a Secret but none can be stolen (because your Secret Zone is full or you already have a copy of all enemy Secrets), a random Secret is destroyed and revealed. Rule Z4: If you would draw a card but have no room for it, its side-effects of drawing (such as Flame Leviathan's or Burrowing Mine's) do not trigger, because it never entered your hand.

Examples:


 * You have Mirror Entity up and so does your opponent. You play a Kezan Mystic. Because the Mirror Entity cannot move to your Secret Zone, it is destroyed and revealed instead. However, if the enemy also had a Duplicate active, the Mystic would steal it with a 100% chance, since Kezan Mystic only destroys Secrets as a last resort.
 * You have 10 cards in your hand and attempt to draw Burrowing Mine. It is revealed and discarded. You do not take 10 damage or draw a new card.

Notes:


 * Before Goblins vs Gnomes, many summoning effects such as Bane of Doom, Imp Master and Ancestral Spirit ignored mortally wounded minions when checking the 7 minion limit, allowing it to be temporarily exceeded. (Internally this is called CAN_SUMMON_MAXPLUSONE_MINION.) As of Blackrock Mountain, this is no longer the case, and mortally wounded minions occupy their space until they are removed from play, with no known exceptions.

Rule Z5: When an Entity moves from one zone to another, the minion's tags (such as Damage, Divine Shield and pending destroy) are reset to a default state. The rules are as follows: Rule Z5a: Play Zone to any other Zone: All Enchantments detached. Rule Z5b: Hand Zone to Play Zone: Enchantments are NOT detached. (However, Mana cost related Enchantments will trigger to detach in the On Play Phase.) Rule Z5c: Deck Zone to any other Zone: Enchantments are NOT detached.


 * Even though Enchantments are detached when moving between zones in this way, if you target a spell or Battlecry at a minion, but before the spell/Battlecry resolves the minion leaves play, the spell/Battlecry can put an Enchantment on the minion in an unexpected Zone (such as the Hand Zone, Graveyard Zone or Deck Zone).
 * The Enchantment will be considered to be in Play, even though the attached minion is not. As a result, the Enchantment will be able to trigger (for example if it is Shadow Madness) and will be able to give your player Spell Damage +1 (Velen's Chosen).

Notes:
 * Before an unknown Patch between 5.0 and 7.0, Deck Zone to any other Zone caused ALL Enchantments to detach. (The Mistcaller was actually coded to create a permanent on-draw trigger, rather than to enchant minions in your deck.)

Exceptions:
 * Notably, the rule that all tags are reset when a minion changes zone seems to be implemented in an ad hoc way. For example, Echoing Ooze's tag change is not cleared if the minion's Battlecry resolves in-hand and is played from your hand, and TO_BE_DESTROYED used to not be cleared when a minion is bounced to the hand or played from the hand (causing the Vaporize/Freezing Trap bug) but now is cleared when the minion is played from the hand.

Rule Z6: When several consequences of Death try to move the dead minion, only the first one works. Others don't work and remain hidden if it's a Secret.

Examples:
 * You play Malorne and Gateway Kodo, then cast Soul of the Forest. Enemy kills your Malorne, and its Deathrattle returns it to your deck. Gateway Kodo remains hidden and Soul of the Forest summons a Treant for you. If you swap the order of Malorne an Gateway Kodo, Gateway Kodo will return Malorne to your hand. Its deathrattle doesn't trigger and Soul of the Forest also summons a Treant.

Note:
 * Resurrecting effects such as Ancestral Spirit and Redemption don't move the dead minion. They summon a new copy of it.

Full Zone Instant Removal
When a minion is destroyed because it tries to move to a Zone that is already full, it is not marked pending destroy. Instead, it is immediately counted as having died and sent to the Graveyard zone. However, its Death Event is correctly included in the subsequent Death Phase, and its consequences of Death queued and resolved at that timing. But since it is immediately removed from play, it is immediately uninteractible, unable to trigger or be triggered. Also, their attributes are reset when moved to the Graveyard zone, like normal death.

Also, note that the order of resolution of Death Events is not the order they are created in (e.g. the order they died in), but the play order of the respective minions. However, Kel'Thuzad will revive the minions in the order their Death Events were created in.

It should also be noted that the Death Event is only created if the minion was in play. If it was in your Hand or in the Graveyard, it goes to the Graveyard and nothing else happens. (If it created a Death Event, Anub'arak dying while your hand is full would create an infinite loop.)

Examples:


 * You play Sylvanas Windrunner, Deathlord and five other minions. Your opponent plays a Knife Juggler. You cast Feign Death. First, the Knife Juggler is instantly killed and removed from play, then a minion is summoned for your opponent due to the Deathlord Deathrattle, but no knife is thrown because the Knife Juggler is already not in play.
 * You play a minion. Your opponent plays a Freezing Trap. You play Blessing of Wisdom on your minion. You wait until you have 10 cards in hand, then attack with the minion. First the Freezing Trap triggers, instantly killing and removing from play your minion. Bleesing of Wisdom does not trigger because the minion is already not in play.

Mana Crystals and mana costs
Rule M1: Your current mana is capped at 10 but has no lower limit. Negative current mana is displayed as 0. Rule M2: Your maximum mana (number of Mana Crystals) is always at most 10 and at least 0. Rule M3: Your current/pending Overloaded Mana Crystals has no upper limit. Rule M4: Gaining or losing maximum mana has no effect on your pending/current Overload. Rule M5: The mana cost of a card has no lower limit. Negative mana costs are displayed as, and use, 0, but help to counteract mana cost increases. Rule M6: When multiple effects change the cost of a card or your Hero Power, they are applied in order of play (Auras and Enchantments having no special priority). One exception is Summoning Portal's aura, which has a very early Priority that makes it considered before ALL other effects. Besides, cards that apply a Mana Cost Aura (Molten Giant, Volcanic Drake, Dread Corsair, etc) have a latest priority. Rule M7: When an effect refers to the cost of casting a spell (such as Summoning Stone or Gazlowe), it means the amount of mana you paid to cast it, not the base mana cost. Rule M8: Kun the Forgotten King gives you 10 temporary mana crystals, but no more than your maximum mana.

Examples:


 * You have an Innervate in hand and 10/10 Mana Crystals and want to do a 11 mana turn. You must spend 1 mana before using the Innervate, or the excess mana will be lost.
 * If you have 10 Mana Crystals and are currently Overloaded for 10, you can still gain mana with Innervate.
 * An Unstable Portal gives you a Wisp. Because this card normally costs 0 mana, it is discounted to -3 but displayed as 0. However, if your enemy plays four Mana Wraiths, the card costs 1 instead of 4 due to this hidden negative cost. (Emperor Thaurissan can similarly reduce your card's cost below 0.)
 * If your opponent plays Loatheb followed by Millhouse Manastorm, your spell cards cost 0 mana. However, if he plays Millhouse Manastorm followed by Loatheb, your spell cards cost 5 mana, due to order of play.
 * If you Shadowstep a Loatheb, then play two Summoning Portals, Loatheb costs 0 mana, not 1, due to Summoning Portal's aura's Priority being first.
 * You can use Felguard's effect to reach 0/0 Mana Crystals, and then The Coin to reach 1/0 Mana Crystals. No matter how many further Felguards you play, you will have 1/1 Mana Crystals your next turn.
 * On turn 2, with 2/2 mana, you play two Dust Devils, giving yourself pending Overload of 4. The next turn, you have -1/3 mana (displayed as 0/3). If you play The Coin, you go from -1/3 to 0/3.
 * If you Overload yourself for 11 with 10 maximum mana, the next turn you have to play The Coin twice to reach 1/10 mana.
 * If you Overload yourself for 10 with 8 maximum mana, the next turn you are at -1/9 mana. If you play Lava Shock for 0, you go straight to 9/9 mana, because -1+10=9.
 * If you play Aviana then Naga Sea Witch, your minions cost 5 Mana. If you play Naga Sea Witch then Aviana, your minions cost 1 Mana. But in addition to this, if you play Aviana after Emperor Thaurissan discounts your cards your minions will cost 1, but if Emperor Thaurissan triggers after Aviana enters play, Emperor Thaurissan's effect will be processed second and your minions will cost 0. This is different to how Health/Attack Enchantments and Auras work - all Health/Attack Auras are processed after Health/Attack Enchantments regardless of play order, but Mana Auras and Enchantments are processed together in play order.
 * Similarly, Maiden of the Lake and Saboteur affect the cost of your Hero Power in the order they were originally played in, with no priority over one another.
 * You gain pending overload of 1 and then destroy a friendly Darnassus Aspirant. Despite the visual appearance of destroying a pending locked mana crystal, next turn you will be overloaded for 1 correctly.

Why available mana can be negative
TODO: What is the interaction between Kun the Forgotten King and Overload?

Tags are values on Entities (such as minions, players and cards) that can have any value between 0 and 2^31 - 1. if their final value would be negative in 32 bit signed arithmetic, it is instead assigned to 0. The tags related to mana and mana costs are as follows:

MAXRESOURCES (player): largest value RESOURCES and 'available mana' can be; it is always set to 10. RESOURCES (player): number of permanent Mana Crystals (also called 'maximum mana'). RESOURCES_USED (player): number of permanent Mana Crystals which are empty or Overloaded. TEMP_RESOURCES (player): number of temporary Mana Crystals (such as due to The Coin).
 * When you pay mana, TEMP_RESOURCES is deducted before RESOURCES_USED is increased by what's left over.
 * Spend mana sets TEMP_RESOURCES to 0 and RESOURCES_USED to the value of RESOURCES.

OVERLOAD_OWED (player): total pending Overload for the next turn. OVERLOAD_LOCKED (player): current Overload.
 * At the start of turn OVERLOAD_LOCKED and RESOURCES_USED are set to the value of OVERLOAD_OWED, and OVERLOAD_OWED is set to 0.
 * Unlocking Overloaded Mana Crystals (such as with Lava Shock) will set OVERLOAD_OWED to 0, decrease OVERLOAD_LOCKED to 0, and decrease RESOURCES_USED by the same amount.

NUM_RESOURCES_SPENT_THIS_GAME (player): total mana paid this entire game. OVERLOAD_THIS_GAME (player): total mana Overloaded this entire game.

COST (card or Hero Power): how much mana you will pay when playing this card. OVERLOAD (card): can be 1 or 0, indicating if this card has the Overload ability or not. OVERLOAD_OWED (card): how much pending Overload playing this card will give you.

'Available mana' does not exist as a tag, but is calculated as RESOURCES + TEMP_RESOURCES - RESOURCES_USED. Because it doesn't exist as a tag, 'available mana' can go negative (such as if you Overload more mana than you will have the next turn): although it will still be displayed as 0 in the GUI, it will affect mana-generating effects like those granting temporary Mana Crystals.
 * Example: If you have 10 Mana Crystals and 11 current Overload, your mana counter will display 0/10 even if your 'available mana' is 10 - 11 = -1. If you play Innervate it will correctly display 0/10, not 1/10.

Conversely, because COST is a tag, even if you reduce a card or Hero Power's cost below 0, its COST will be clamped to 0, so you won't 'gain mana' by playing it.

Drawing a Card
Rule DC1: When you draw a card, if you have room, it enters your hand and is immediately resolved (according to the below rules). When multiple cards would be drawn simultaneously, the number of cards that would be drawn is calculated, then each one is drawn and resolved in some sequential order. (For example, Coldlight Oracle always draws two cards for its controller first.) Rule DC2: Some effects (Chromaggus, Shadowfiend) trigger when a card is drawn. They trigger in order of play. Then, the card may have an effect when drawn (Sea Reaver, Flame Leviathan, Ambush!, Burrowing Mine, Fatigue, etc). This effect resolves now. When this is complete, the card draw has been resolved. Rule DC3: Some effects (Gnomish Experimenter, Holy Wrath, Far Sight, Call Pet) draw a card, then do something with that card. These effects wait for the card draw to resolve before continuing. Holy Wrath does require the card to successfully enter your hand. Rule DC4: A card is only considered drawn if it moves from the top of your deck to your hand. If your hand is full, the card is not drawn, nor is it discarded (such as for Tiny Knight of Evil or Fist of Jaraxxus), it just goes to the Graveyard. Rule DC5: An effect is not considered to have drawn a card if it was drawn indirectly (for example, if Varian Wrynn draws Ambush! which itself draws a minion, the minion is not put in play).


 * Note that Chromaggus and Mimic Pod cannot copy buffs or enchantments.
 * The essence of Rule DC2 is Play triggers' priority to Hand triggers. For more information, see The Order of Battlefield, Hand and Deck Triggers section.
 * Auras that change cards' cost don't affect the damage dealt by Holy Wrath. But Barnabus the Stomper, Renounce Darkness and Shadow Fiend can reduce the damage.
 * Different from drawing, when you discard multiple cards, they will move to Graveyard together. Then each card's discard effect is queued and resolved, left to right.
 * Similar to Rule DC2, when you discard a card, battlefield triggers such as Tiny Knight of Evil work. Then the card's effect when discarded is resolved such as Silverware Golem.

Examples


 * You play Chromaggus and Gnomish Experimenter, set both to 2 Health, then draw Flame Leviathan. First Chromaggus triggers and puts a copy of Flame Leviathan in your hand. Then the drawn Flame Leviathan triggers and deals 2 damage, mortally wounding both Chromaggus and Gnomish Experimenter. Then Gnomish Experimenter triggers and turns the drawn Flame Leviathan into a Chicken. Finally the Phase is over and death processing happens, killing and removing from play Chromaggus and Gnomish Experimenter.
 * You play Varian Wrynn. The first card is Ambush!, which triggers and draws a Boulderfist Ogre. Because Ambush! drew the Boulderfist Ogre, Varian Wrynn does not count it as one of his 3 cards or put it into play.
 * You play Shadowfiend and Chromaggus, and draw a Leper Gnome. First Shadowfiend discounts the drawn Leper Gnome to 0, then Chromaggus adds a 1 cost Leper Gnome to your hand. (Chromaggus similarly does not copy the cost reductions of Call Pet or Far Sight.)
 * You play Shadowfiend, Mechwarper then Holy Wrath. The drawn card is a Spider Tank. Shadowfiend triggers and reduces it to 2 cost, then Holy Wrath continues and deals 2 damage to its target. Finally the Spell Text Phase is over, Auras update and the Spider Tank now costs 1 Mana.
 * You play Holy Wrath. The card drawn is Ambush!, which triggers and draws a Boulderfist Ogre, then Holy Wrath continues and deals 3 damage (the cost of Ambush!).
 * If you have 9/10 cards in your hand when Gnomish Experimenter's Battlecry resolves, and you also have Chromaggus in play, since the drawn card enters your hand before any on-draw triggers run, Chromaggus won't put a copy of the minion in your hand. Then Gnomish Experimenter triggers and transforms the topdecked card.

Exceptions:


 * Tracking does interact with on-draw triggers.
 * Daring Reporter has the same priority as 'the card may have an effect when drawn'. For example, if Sea Reaver is drawn, the order of triggering of Daring Reporter and Sea Reaver is determined by the Dominant Player Bug.
 * The expression 'Auras that change cards' cost don't affect the damage dealt by Holy Wrath' is not completely right. That is because Aura Update is not run in-between. You control a Emerald Hive Queen and Dragon Egg, and your Holy Wrath draws a Flame Leviathan. Flame Leviathan first deals 2 damage to all characters, causing Dragon Egg summoning a Black Whelp. The cost now is affected by Emerald Hive Queen, and Holy Wrath deals 9 damage.

Damage and Healing
Rule DH1: When an area of effect Damage or Healing effect happens, all of the Damage/Healing Events are created in play order, then all of the Damage/Healing Events are resolved (queuing and resolving triggers) in play order. Rule DH2a: When a Damage/Healing Event is created: Apply Auchenai Soulpriest. Then apply Spell Damage/Fallen Hero/Arcane Amplifiers. Then apply Prophet Velens. If the target is Immune or the Damage Event's proposed damage is 0, the Damage Event is prevented. Then if the target has Divine Shield, the Divine Shield is removed and the Damage Event's proposed damage is reduced to 0. Then queue and resolve Predamage triggers (see Rule DH7). Then the Character's current Health+Armor is reduced by the Damage Event's proposed damage. (If the target is affected by Commanding Shout, its current Health is prevented from dropping below 1.) Rule DH2b: When a Damage/Healing Event is resolved: If it was prevented, or if it did not change the Character's current Health+Armor total (including due to Divine Shield and Commanding Shout), it will not run any triggers. Otherwise, they queue and resolve in play order.

Rule DH3: Some Damage effects sound like they should be area of effect (and therefore create all Damage Events before any of them resolve), but actually resolve each Damage Event as soon as it is created in play order. These are: Lightning Storm, Elemental Destruction, Dark Iron Skulker, Lightbomb. However, these effects still figure out the set of minions they will damage before beginning to damage anything. Rule DH4: Two-step spells (such as Light of the Naaru, Mortal Coil, Bane of Doom, Slam, Bash, Bouncing Blade) that create one or more Damage/Healing Events before then querying the target's condition, must resolve the Damage Event BEFORE they query the target's condition. Rule DH4b: Some other Two-step spells exist: Holy Nova creates and Resolves all Damage Events, then creates and resolves all Healing Events (even if the Healing Events are turned into Damage Events by Auchenai Soulpriest). Blizzard creates and resolves all Damage events, then freezes all enemy minions (even undamaged ones). Cone of Cold creates and resolves all Damage events, then freezes the minions it damaged. Rule DH4c: One spell, Imp-losion, deals damage then queries how much damage was dealt. Divine Shield sets the damage dealt to 0 and Immune prevents the damage, however Commanding Shout does not modify how much damage was considered to be dealt - therefore the normal number of Imps will be summoned. Rule DH5: Some effects create Damage Events out of order of play, likely due to a bug - and therefore they also resolve out of order of play. Swipe damages the target Character, then all other enemy Characters in reverse play order, then resolves all Damage Events. Explosive Shot, Cone of Cold and Powershot damages minions in the order center, left, right. Rule DH6: When a minion is the source of a Damage Event, even if the Damage Event's proposed damage is 0, it loses Stealth. (If the Damage Event is prevented, it does not lose Stealth.)


 * (Your Heroes are older than every minion. The Hero of the Dominant Player is older than the Hero of the Secondary Player.)
 * Note that minions do not die the moment they are mortally wounded (0 or less Health). For more information, see Death Phases and consequences of Death.
 * Note that damage from two Characters engaging in Combat is not based on play order, - the attacker always damages the defender first. For more information, see Combat.
 * Note that Immune also prevents enemy targeting, like Stealth. It does not prevent any other kind of interaction, including healing.
 * Note that Stealth is also lost when a minion declares an attack, even if the combat is cancelled or it would fail to create a Damage Event due to losing all its Attack. For more information, see Combat.
 * The definition of 'apply Auchenai Soulpriest' is 'If the Event's source's controller also controlled an unsilenced Auchenai Soulpriest since the last Aura Update (Other) step, replace the Healing Event with a Damage Event having proposed damage equal to its proposed healing'. (The definition of 'apply Prophet Velens' is similar.)

Examples:


 * If you cast Circle of Healing with damaged minions and Shadowboxers in play, all of the minions will be healed before the Shadowboxers trigger on each Healing Event and deal damage, preventing them from damaging a minion that would later be healed.
 * If you cast Flamestrike while your opponent has two Armorsmiths, the Armorsmiths will be mortally wounded but remain in play, triggering on each Damage Event and giving your opponent's Hero 4 Armor before the spell resolves and the Armorsmiths die and are removed from play.
 * If you play Light of the Naaru, restoring an enemy minion to full health, but also triggering an allied Shadowboxer to damage the target enemy minion, Light of the Naaru's second step then runs and sees the target is damaged, summoning a Lightwarden.
 * If you cast Holy Nova while your opponent has an Imp Gang Boss and a Knife Juggler, because the Damage Events are Created and Resolved before the Healing Events are Created and Resolved, the extra damage caused by the knife from the summoned Imp may be healed by the second step of Holy Nova.

Predamage Triggers
Rule DH7: Just before a Damage Event is created, Predamage triggers will queue and resolve in play order. They will stop triggering if the Damage Event is prevented, as there is nothing to do. The full list of Predamage triggers is Bolf Ramshield, Ice Block, Animated Armor. Additionally, Animated Armor has an early priority. Rule DH7b: Bolf Ramshield's effect is to prevent the Damage Event, then create a Damage Event whose source is still the original source but target is Bolf Ramshield, and whose proposed damage is the same as the original Damage Event's. Rule DH7c: Animated Armor's effect is to lower the Damage Event's proposed damage to 1. Rule DH7d: Ice Block's effect is, if the Damage Event's proposed damage is currently greater than or equal to your Hero's current Health, to prevent the Damage Event and create an Enchantment attached to your Hero which says "Become Immune until the turn ends."


 * Because Bolf Ramshield creates a new Damage Event with the source being the original source, if a minion with a 'when this minion deals damage' trigger such as Queen of Pain, Water Elemental and Emperor Cobra has its combat damage prevented by Bolf Ramshield, the trigger will still run.
 * Like other triggers, Bolf Ramshield and Animated Armor can trigger even if mortally wounded for as long as they are in play.

Examples:


 * If you play Ice Block and Animated Armor, your Hero is at 4 Health and your opponent deals 4 damage to your Hero, regardless of order of play, Animated Armor triggers and reduces the incoming damage to 1 before Ice Block checks for the damage being lethal (and since it isn't, it remains intact).
 * If you have multiple Bolf Ramshields in play, the first one to enter play will trigger and intercept the damage when your Hero takes damage.
 * If you have Animated Armor and Bolf Ramshield, regardless of order of play, your Bolf Ramshield will intercept 1 damage.
 * If you adapt Bolf Ramshield to gain Poisonous, it won't be killed by its own effect.

Notes:


 * Prior to Patch 5.0.1.13030 (2016-06-01), Animated Armor did not have an early priority, and would trigger in order of play with the other predamage triggers.

Cursed Blade
Rule DH8: Cursed Blade's effect is to double the proposed damage of Damage Events targeting your Hero (whenever queried by a Predamage trigger or when your Hero takes the damage).


 * This leads to the following interactions:
 * The final damage you take will be doubled, after all modifiers (like Spell Damage, Prophet Velen and Fallen Hero/Arcane Amplifier) are taken into account.
 * If you have Cursed Blade and Ice Block, Ice Block will take into account the double damage from Cursed Blade when deciding to trigger or not.
 * If you have Cursed Blade and Bolf Ramshield, Bolf Ramshield takes double damage when intercepting, regardless of play order.
 * If you have Cursed Blade and Animated Armor, Animated Armor will set the Damage Event's damage to 1, but Cursed Blade's effect will double its damage whenever it is read, so you will still take 2 damage (Bolf will still intercept 2 damage, etc). (In addition, normally Animated Armor does not trigger if you take 1 damage, but Cursed Blade's effect doubles the reported damage to 2, so Animated Armor will trigger for no effect in this scenario.)

Death Event Cache
Rule DEC1: Hearthstone keeps track of every Death Event that has been created this game in the Death Event Cache. It remembers the Entity ID that died, its controller when it died, and what turn it died on. Rule DEC2: If the same minion dies more than once (for example if it's the same Malorne), each Death Event is added to the Death Event Cache separately. Rule DEC3: Cards that check if a minion has died this turn/this game (Feugen, Stalagg) and cards that resurrect minions that died this turn/this game (Resurrect, Kel'Thuzad, N'Zoth, the Corruptor, Anyfin Can Happen, Doomcaller) do not check the Graveyard Zone. They check the Death Event Cache. Rule DEC4: Resurrect effects summon new, fresh copies of minions based on the Death Event(s) they select, and do not remove the Death Event from the Death Event Cache. Except for Kel'Thuzad who uses order of play, Death Events are selected in random order.


 * If a minion goes to the Graveyard Zone in any way besides dying (milled from deck, discarded from hand, etc) it never died, so it does not get added to the Death Event Cache.
 * Entries in the Death Event Cache are never removed, even if a Resurrect effect selects that Death Event.
 * Minions that leave the Graveyard Zone don't remove their Death Event from the Death Event Cache (for example if it's Malorne, Anub'arak or The Skeleton Knight).
 * The Entity ID is used to find out what kind of card died. For exactly one card - Shifter Zerus - the Card ID it was when it died might not be the Card ID it is now. It will use the Card ID it is now.

Examples:


 * You play and kill your Malorne 3 times, then play N'Zoth, the Corruptor. Three Malornes will be summoned by N'Zoth's Battlecry. Resurrect and Kel'Thuzad also bring back Malorne.
 * Your C'Thun is discarded, milled, Entombed/Mind Controlled and dies for your opponent or Polymorphed and dies as a Sheep. You play Doomcaller. You never had a C'Thun die, so nothing happens.
 * Your C'Thun dies. You play two Doomcallers. Each one shuffles a C'Thun into your deck.
 * You play three Kel'Thuzads and kill one and end your turn. Each living KT sees the KT that died this turn and resurrects a copy of it, so you now have four KTs in play.
 * You play a minion, give it a Deathrattle (such as Ancestral Spirit) and it dies. You play N'Zoth, the Corruptor. The minion is not brought back to life, because the Death Event Cache does not record the state it died in, only what kind of minion it was.
 * Using Violet Teacher and Knife Juggler, Entomb targets a Shifter Zerus that dies before Entomb resolves. When this Shifter Zerus is later drawn, it is allowed to transform into another minion. When Resurrect or N'Zoth, the Corruptor is played and considers Shifter Zerus's Death Event, it will look at what Card ID Shifter Zerus is now, and thus resurrect the minion it has changed into in the hand.
 * If you play and kill Malorne, replay Malorne, silence Malorne then play N'Zoth, the Corruptor, a new Malorne will be summoned. This is because the Card ID of the Entity ID that died, not the current state including silence, added Deathrattles, etc, is checked to determine what to resummon.
 * Resurrect effects will resummon Weasel Tunneler for who it originally died for, not for who controls the Weasel Tunneler now. This is because the Death Event Cache records the controller at the time of death.

Spell Damage
Spell Damage is unlike Auras - it does not update when each outermost Phase resolves and Hearthstone updates Auras. Rather, it updates constantly - it is always the most up-to-date value.

Examples


 * You Earth Shock your own Wrath of Air Totem. The totem is silenced, removing Spell Damage +1, then Earth Shock deals 1 damage, not 2.
 * You Earth Shock an enemy Jungle Moonkin. The Jungle Moonkin is silenced, removing your Spell Damage +2, then Earth Shock deals 1 damage, not 3.
 * You play a Frigid Snobold into an enemy Mirror Entity followed by Snipe. Snipe will take into account the new Spell Damage +1 added in the same Phase and deal 5 damage, not 4.

Notes


 * Jungle Moonkin gives your opponent Spell Damage +2 via an indirect mechanism.

Extra Turns and Temporary Effects
There are 2 effects giving players extra turns in Hearthstone (excluding those in Adventure Mode), and here are their rules:
 * Temporus's battlecry gives your opponent an extra turn before his next turn starts, and gives you an extra turn after a series of opponent's turns (perhaps more than 2).
 * Time Warp gives you an extra turn immediately this turn ends.

In general, temporary effects only work in one turn. However, effects that read 'In your opponent's next turn...' keep working until the end of a series of opponent's turns， including Millhouse Manastorm, Saboteur and Loatheb.

Examples: (A refers to your turn, and B refers to opponent's turn.)
 * You have Brann Bronzebeard and play Temporus and Time Warp. Regardless of play order, the following turns are ABBBAAA.
 * You play Temporus and then your opponent also plays Temporus. The following turns are BBAAABB (including your opponent's this turn).

Visual appearance of Player Actions
When you perform a Player Action, Hearthstone processes the entire outcome server-side and then slowly displays the result in client-side animation. With the exception of conceding, Hearthstone shows the initial result of all Player Actions (summoning a minion to the board, flipping the Hero Power, flipping the End Turn button, etc) but in reality, Hearthstone has processed your Player Action at the appropriate time server-side - after all previous Player Actions have resolved.

You can tell when Hearthstone server-side finished processing the outcome because your valid Player Actions will be highlighted in green once more (and if you have none, you will hear 'Job's done'). This allows you to tell ahead of time things like 'Did this minion die?' (that minion is not highlighted green) or 'Did the game just end?' (no actions are presented) or 'Are all enemy minions dead?' (an enemy minion targeting spell in your hand is not highlighted green). The only reason to wait through animations is if a randomized outcome is important for your decision making - such as the Deathrattle of Piloted Shredder.

Some consequences and oddities of Player Actions ignoring animations:
 * If a Mechwarper is alive, even if the mana cost has not been updated, Mechs that you can play are highlighted in green.
 * If you return a minion to your hand such as with a Youthful Brewmaster, it will be highlighted in green even before visually turning into a card. If you interact with it, the game will play it from your hand, a useful time-saver.
 * If you draw cards and immediately hear 'Job's done' you know none of them are playable this turn.
 * Technically you can target an enemy minion spawned by a Deathrattle, play a card drawn, etc the moment the server has processed the outcome - but until the animations of client-side Hearthstone render it, there is no way for the user to do so without using an external program or a hack.
 * "Cast X random spells" effects can make visual updates based on changes in available mana before the actual display of available mana is updated. Example: Puzzle Box of Yogg-Saron casts Shadowform as its first spell, replacing the Hero Power with Mind Spike. The new Hero Power is immediately highlighted green despite the client still displaying 0 available mana, because the Puzzle Box will cast Nourish later, generating 2 available mana.

Turn timers
Whenever a player's turn begins (including the Mulligan turn), the Hearthstone server gives them 75 seconds from that exact point in time until their turn ends. (It was 90 seconds during Beta.) This time limit totally ignores animations because the server does not simulate them. This means that the animation of start of turn triggers, drawing a card at the start of your turn, the 'Your turn' splash, etc. eat into the 75 seconds.

In addition to this, when the Server sees that the end turn button is hit (or the timer expires), the other player's turn immediately begins - even if one or both player's clients is still animating the results of player actions taken during that turn. Again, this is because the server does not simulate or care about actions. This means that if you queue up many long, complex animations then hit the end turn button before they finish, all of that animation time eats into your opponent's 75 seconds.

Being able to 'eat into' following turn timers has no upper bound - if you queue so many animations that 75 seconds pass after ending your turn, your opponent's entire next turn will be skipped, and it will be your turn again. If you queue an arbitrarily large amount of animation time, an arbitrary amount of turns may be skipped, causing an extreme amount of graphical effects and glitches when Hearthstone tries to show the results of all the turns being skipped at once.

Nozdormu and AFK

Nozdormu's effect is to reduce turn timers from 75 seconds to 15 seconds. (This is implemented by changing the TIMEOUT tag between these two numbers - whenever it changes, the timer is reset to about its full remaining value, allowing you to make a 5 minute long turn by repeatedly playing and removing from play Nozdormu. ) Otherwise, all the rules are the same. But because it is a lot easier to queue 15 seconds of animations after your turn, it is a lot easier to skip your opponent's turn with Nozdormu out than without.

Notably, because AIs instantly queue all their actions and end their turn, without having to watch any animations, if Nozdormu gets into play while fighting against an AI, defeat due to every one of your turn timers being eaten up is almost certain.

AFK is an Enchantment a player gets if on their last turn they performed no player actions, not even hitting the end turn button. It reduces that player's turn timer to 10 seconds until the next time they take a player action.

Speeding up animations and countering Nozdormu

However, there is a way to speed up animations in Hearthstone. Whenever your opponent plays a card or activates a Hero Power, a Secret is revealed or Cursed! triggers in your hand, you can click on the big card pop-up in the top left of your client, making it vanish instantly and the following animation start immediately. Each time you do this, it saves 1-2 seconds, and doing this when Nozdormu is in play will counter tactics where your opponent attempts to eat into your entire turn timer, giving you just enough time to perform player actions during your turn, and perhaps destroy Nozdormu to end the combo.

Slush time

An undocumented mechanic of Hearthstone is slush time, which is added to the next turn timer whenever certain animations happened on the previous turn. Currently, it is unknown what the full list of animations that add slush time is, and how much slush time they add, but two are known: Youthful Brewmaster effects and Joust effects add their full animation length as slush time, preventing Nozdormu in combination with these cards from being used to eat the turn timers of, and thus defeat, players unaware of the 'card clicking' trick.

There is a tag called TURN_TIMER_SLUSH, but it is currently not displayed in power.log.

Glossary

 * Character: A minion or hero.
 * Entity: Anything that exists in the game of Hearthstone - a character, weapon, Hero Power, Secret, card, Deathrattle, triggered effect, Enchantment, Aura, spell being played or disembodied 'effect' (such as Loatheb's cost increase that lasts a turn or Dragon Consort's cost reduction that lasts indefinitely - while invisible, they have similar properties as other Entities, for example the order you play Loatheb and Millhouse Manastorm in is relevant).
 * Player Action: Attacking with a character, playing a card, using a Hero Power, hitting the end turn button or conceding.
 * Trigger: Anything that triggers in reaction an Event - any triggered effect, Secret or Deathrattle.
 * Event: A single change in the game state. Can have triggers Queued in reaction to it - a Death being considered, Healing, Damage, Summon, drawing a card, a specific named Phase of a Sequence and so on.
 * Resolve: When Hearthstone finishes processing all consequences (except Deaths, which do not happen until the outermost Phase ends) of an Event. Defined recursively - For example, if a Knife Juggler's trigger triggers a Grim Patron, the Knife Juggler's trigger is not resolved until the Grim Patron's trigger and all its consequences are resolved first. Can be nested arbitrarily deep.


 * Order of play: The order in which each Entity was put into play. Ties are broken between Entities by ordering them from first to most recent to enter play.
 * More specifically, each Entity has a timestamp associated with it. The timestamp is updated every time the Entity is generated or moved to the Play zone.
 * Attached Enchantments use their own timestamp, not the timestamp of the Entity they're attached to. This is used for when their trigger triggers (Shadow Madness, Power Overwhelming, etc) and also for when their Enchantment is processed in the Enchantment List.
 * There is only one exception to the above rule - the Enchantments created by an Aura (such as the +1/+1 on each other minion due to Stormwind Champion, or the +5 Mana Cost on each enemy spell due to Loatheb's Enchantment) have the timestamp of the Aura bearing Entity, NOT the timestamp of the individual Aura-effect Enchantments entering play.
 * In addition, note that Priority takes precedence over Order of play, and the Dominant Player Bug takes precedence over Priority.


 * Phase: A Phase begins when multiple Events are raised simultaneously, or when multiple triggers respond simultaneously to a common Event, or as part of a Sequence. (Phases can be nested.) When the outermost Phase resolves, we run the following Steps: Aura Update (Health/Attack), Death Creation Step, Aura Update (Other). Then if any Deaths occurred, a Death Phase starts, resolving Death Events in order of play, for each one queuing and resolving all on-death triggers (including Deathrattles and Secrets). Since a Death Phase is an outermost Phase, it will have its own Steps after it resolves, and can be followed by another Death Phase, and so on. This continues until there are no new Deaths - then we finally proceed to the next named Phase of the Sequence.


 * Step: Not a Phase. (Everything that is called a Phase is called a Phase because of the steps that run after it, if it's the outermost Phase. If we don't do that, it's called a Step.)
 * Sequence: A series of outermost Steps/Phases that must be resolved one after the other.


 * Aura Update: Refers to both Aura Update (Health/Attack) and Aura Update (Other) happening. (Sometimes in Hearthstone these can happen without an intervening Death Creation Step, such as between the two Battlecries when Brann Bronzebeard is in effect.)
 * Aura Update (Health/Attack): Runs before the Death Creation Step after each outermost Phase resolves, and at a few other timings. Health/Attack Auras are recalculated, and moved in each Entity's Enchantment List to the end. (Note that Enchantments like Equality apply immediately, and therefore may briefly apply 'out of order'.) Then, every Entity's Health and Attack values are recalculated.
 * Death Creation Step: Hearthstone looks for all Characters that are mortally wounded or pending destroy and, in order of play, sends them from play to the graveyard and creates Death Events for each. (During the next Death Phase, the Death Events will be resolved in order of play.)
 * Aura Update (Other): Runs after the Death Creation Step after each outermost Phase, and at a few other timings. The following Auras update: Baron Rivendare, Auchenai Soulpriest, Brann Bronzebeard, Mal'Ganis's Immune effect, Prophet Velen.
 * Priority: A small number of triggers and auras have a Priority that makes them always act first or act last, ignoring normal order of play. Any card can be set to have any priority and it depends on what the designer intends to have happen. There is a base set of rules that the server uses to determine order of execution, but on top of this is a layer that allows cards to execute at earlier or later priorities relative to other cards of the same type. Most cards will not utilize the priority layer and will execute in the order they were played. For more information on Priority, see the official dev comments made by Software Engineer syah_hs here.
 * Queuing: At the start of a Phase its simultaneous Events or triggers are queued first by Priority then by Order of play. After Queuing resolves the Queue cannot be added to, removed from or re-arranged. However, no matter how recently a trigger or Secret appeared prior to a Queue, it may be included. Events inside of a Phase may have their own Queues.
 * Targeting condition: For a targeting Battlecry, Spell or Hero Power, a condition required to be true of the target when you consciously take the action. (If the condition is later invalid, due to the target changing, triggers changing attributes of the target or the action being copied by Djinni of Zephyrs, the targeting condition is not checked a second time.) (Note that targeting conditions prevent targeting. As a result, spells that say 'X. If Y, Z.' like Demonfire, are checked when the spell resolves, not as a targeting condition.)
 * Queuing condition: A condition that is checked when the queue is being populated; if false, the trigger is not added to the queue.
 * Trigger condition: A condition that is checked just before the trigger begins to resolve.
 * Abort: A Queued trigger may decide not to go off if at the time of triggering it is no longer valid or not useful enough. Freezing Trap aborts if its target is mortally wounded or removed from play, Noble Sacrifice aborts if there's no room, Grim Patron aborts if it is now mortally wounded, Mimiron's Head aborts if there are no longer 3 Mechs and so on.
 * Mortally wounded: An Entity reduced to 0 or less Health/Durability this Phase. Negative/hindering effects like Knife Juggler and most negative/hindering Secrets check for mortally wounded minions and ignore them/do not target them. For more information, see Death.
 * Pending destroy: An Entity hit with a destroy effect/equipped over this Phase. Effects that ignore/include mortally wounded also ignore/include pending destroy.
 * Death, kill: Once the outermost Phase resolves, during the Death Creation Step, Hearthstone kills all mortally wounded and pending destroy Entities, rendering them dead. Because a Death is an Event, a new Phase begins where all simultaneous Deaths are Queued. Dead characters instantly cease to exist - removed from play, unable to trigger or be triggered, all attached enchantments and auras instantly removed. (While triggered effects like Knife Juggler appear to ignore 0 Health characters, this is because they are specifically coded to ignore them - they are not dead yet for all intents and purposes.) Death is the only Event that is not resolved in the middle of a Phase.
 * In play: An Entity that is currently on the board, i.e. not dead. (Can trigger and be triggered, applies its Auras to other Entities, interact and can be interacted with, and takes up space e.g. for the purposes of attempting to summon new minions/put into play another Secret).


 * Force play: Deathlord, Voidcaller, Alarm-o-bot and Ancestor's Call do this. The moving of a minion from your hand OR deck into play. Does nothing (Rather than kill the minion) if there is no room.
 * Forced Death Phase: Poison Seeds, Reincarnate and Mimiron's Head do this. A Death Phase that forcefully appears inside of a Phase, therefore any Deaths caused by it are not resolved until the outermost Phase ends.
 * Summon Resolution Step: A step at the end of an outermost Phase, surrounded by two instances of Aura Update (Health/Attack) (and therefore before the subsequent Death Creation Step) where Steward of Darkshire, Starving Buzzard, One-eyed Cheat, Undertaker, Commanding Shout and Knight of the Wild trigger on the Summon Events of minions that have entered play since the last Summon Resolution Step.


 * Humble safeguard: Minions are not allowed to trigger on themselves entering play. (Note that they can trigger on consequences of themselves entering play - for example if you play Illidan Stormrage followed by Knife Juggler, the Knife Juggler will trigger off of the Flame of Azzinoth created by Illidan Stormrage in reaction to itself being played.)
 * Double safeguard: Minions are not allowed to trigger twice on the same Event. In addition, Clumsy and Mogor the Ogre can't trigger on a given attack if they failed the 50% chance already.


 * Tag: Describes one aspect of the state/identity of an Entity. Has a name (such as ZONE) and a value (which can be an integer, boolean (0 or 1) or string).
 * Tag numerical limits: 32-bit signed integers are used to represent the numerical values of Tags. (Examples of numerical valued tags are HEALTH, ATTACK and DAMAGE.) These range from [-2^31, 2^31 - 1] while the value of a Tag is being recalculated. However, if a Tag would be assigned a negative value, it is assigned 0 instead. Examples:
 * If you have a Lorewalker Cho with 2^30 HEALTH and cast Divine Spirit on it, its HEALTH becomes 0 (because 2^31 assigned to a 32-bit signed integer overflows to a negative number, which is capped to 0).
 * If you play Shrinkmeister on a Wisp, it becomes a 0/1. If you end your turn, it becomes a 1/1. If instead you target it with Abusive Sergeant, it becomes a 1/1 also.
 * If you have a Wisp in your hand and a Pint-Sized Summoner and Mana Wraith in play, regardless of order of play, it costs 0 Mana to play.
 * If you have a Gahz'rilla and double its Attack enough times, the Attack value will overflow and become negative, meaning that when ATTACK's value is assigned it will be assigned a 0. In addition, adding small amounts of Attack (such as with Abusive Sergeant) do nothing, as the intermediate calculated value is still negative. Double the attack even more, and it will occasionally stop being negative and start being a very large positive value again. Finally after enough doublings,, it will eventually become 0 due to the limits of 32-bit arithmetic, and after this, adding Attack with Enchantments will succeed.
 * Using many Prophet Velens, you can double the damage of a spell so much that its final damage becomes nonsensical unless you use the properties of 32 bit arithmetic to calculate it.
 * If you have two minions with exactly 2^30 Health, and play a Void Terror between them, it will create an Enchantment that gives exactly 2^31 Health... except that 2^31 gets clamped to 0, so it creates an Enchantment that gives exactly 0 Health, and thus the Void Terror's Health will remain at 3.
 * Note that if a calculation relies on the value of another tag (for example, your Hero's Attack value is the sum of all Hero Attack buffs plus the Attack of your weapon), it uses the final value of that tag - so if it was negative and clamped to 0, 0 is used.

Esoteric rulebook
Mechanics that are rarely seen yet have some general applicability and/or are arguably bugs will be featured here instead of in the main advanced rulebook.

Forced Death Phase
Mimiron's Head, Poison Seeds, Reincarnate, Blood of The Ancient One, Ravenous Pterrordax, Defile, Yogg-Saron, Hope's End and Lynessa Sunsorrow all have in common that they force a Death Phase to begin inside of the Spell Text Phase/"Start of Turn Phase"/"End of Turn Phase", with a Death Creation Step just before it that kills and removes from play mortally wounded and pending destroy minions. New minions cannot be summoned correctly without this mechanic. If you remember how Phases work, then you know that normally a Death Phase cannot start inside of a Phase - and indeed, once the Forced Death Phase ends, no follow-up Death Phases can be scheduled until the outer Phase ends, so additional Deaths remain un-processed until then. Besides, Servant of Yogg-Saron and Tortollan Primalist can also insert a Death Phase in their Battlecries when comboed with Brann Bronzebeard.

However, some cards don't apply this mechanic despite having similar descriptions with cards mentioned above. They are Invocation of Air from Kalimos, Primal Lord and Spreading Plague.

New in League of Explorers, Djinni of Zephyrs copying Reincarnate triggers a Forced Death Phase.

The steps that run when a Forced Death Phase is executed are as follows:


 * Aura Update (Health/Attack)
 * Summon Resolution Step
 * Death Creation Step
 * Aura Update (Other)
 * Death Phase
 * Aura Update (Health/Attack)
 * Summon Resolution Step
 * Aura Update (Other)
 * Next step in the original phase

Note that Aura Update (Other) runs after the Death Creation Step and before the Death Phase, and Aura Update (Health/Attack) does not run after the Death Creation Step and before the Death Phase. This means that the Aura updates relative to a Forced Death Phase are similar to those before a normal Death Phase.

Examples


 * You play a Haunted Creeper then Explosive Sheep. Your opponent plays Poison Seeds. Your minions are marked pending destroy, then a Forced Death Phase runs where two Spectral Spiders are summoned, then the Explosive Sheep's Deathrattle mortally wounds them. But the new Deaths are not processed yet - the rest of the spell continues, summoning Treants, then finally the Spell Text Phase ends and the Spectral Spiders are killed.
 * Both players' boards are full of Boom Bots. You play Mimiron's Head. Both players pass. When Mimiron's Head triggers, a Forced Death Phase runs where all friendly mechs are removed from play, and consequences of death subsequently run - in this case, the Boom Bot Deathrattles go off, mortally wounding enemy Boom Bots. However, the enemy Boom Bots remain mortally wounded until the end of the Start of Turn Phase, before the Death Creation Step finally runs again and the enemy Boom Bots' Deathrattles go off, able to target V-07-TR-0N, which they wouldn't have been able to if Forced Death Phases repeated until no further the Death Creation Step occurred.
 * Your opponent has a Zombie Chow and Auchenai Soulpriest. You play Poison Seeds. Regardless of order of play, you get healed by the Zombie Chow.
 * You have a damaged minion and a Stormwind Champion. You cast Reincarnate on the Stormwind Champion. Your damaged minion does not gain 1 Health.

Notes


 * Between the Naxxramas expansion and the Goblins vs Gnomes expansion, Kel'Thuzad also used a Forced Death Phase before then re-summoning everything that had died this turn. This made it possible to, for example, have Ragnaros mortally wound Kel'Thuzad then Kel'Thuzad would allow himself to die then resurrect himself.
 * During Patch 4.2.0.12051 (2016-03-14), Forced Death Phase mechanics no longer ran a Death Phase after their Death Creation Step, meaning the Deathrattles of the minions they've killed were postponed until after the rest of the effect finishes (minions being summoned, etc). As of Patch 4.3.0.12266 (2016-04-14) this has been reverted.
 * Before K&C there are no Aura Update or Summon Resolution Step between Forced Death Phase and the next step.

Miscellaneous weapon information

 * Weapons can go to negative Durability before breaking in the following Death Creation Step - for example by using Dread Corsair and Brann Bronzebeard.
 * If your Weapon has less than 0 Attack (such as by using Gorehowl and Spiteful Smith) (still displayed as 0) and you cast Heroic Strike, your Hero will display 4 Attack, not 3. This means that the Weapon Attack and Hero Attack are calculated and added separately.
 * Buccaneer triggers the exact moment a weapon is equipped (not played) - not on any sort of delay.
 * Cursed Blade's effect is similar to Aura(Health/Attack). For example, attacking into an enemy Abomination with the last charge of your Cursed Blade will cause you to take 4 damage from the Deathrattle, because the first Weapon Update Step runs BEFORE Cursed Blade leaves play in the Death Creation Step, and the next Weapon Update Step is not until after the following Death Phase. Using Sabotage on an enemy Cursed Blade and Abomination, the Abomination Deathrattle also deals 4 damage.
 * Before K&C if you have a Deathrattle weapon you have just equipped immediately replaced, such as by Brann Bronzebeard plus Blingtron 3000, its Deathrattle will not work.

Destroy effects in all zones
It has been said that a Destroy effect hitting an Entity actually just sets it pending destroy/TO_BE_DESTROYED, a flag that is checked in the next Death Creation Step, and has the same effect as the Entity having 0 current health. However, this is only true for minions in the Play Zone being Destroyed. A full list of effects is as follows:


 * Minion in Play Zone: Set pending destroy.
 * Hero in Play Zone: Set pending destroy. When the Hero actually dies, your Player Entity's PLAYSTATE tag is set to LOSING, and the next time Hearthstone checks for win/loss/draw you lose the game.
 * Weapon in Play Zone: Set pending destroy. If it existed since the last Weapon Update Step, its Deathrattle will run the next Weapon Update Step (see previous section for more information).
 * Secret in Play Zone: Dies and goes to the Graveyard. (Happens when Counterspelled, Flared, stolen by a Kezan Mystic when there's no Secret that can be validly stolen and when the Secret triggers)
 * Minion/Hero in Graveyard Zone: No known effect.
 * Minion/Hero in Setaside Zone: Goes to the Graveyard. No other known effects
 * Any card in Deck Zone: Goes to the Graveyard. No other known effects.
 * Any Card in Hand Zone: Goes to the Graveyard. Counts as a discard and does not create a Death Event, so no Deathrattles/on-death triggers run, Volcanic minions (and similar effects) don't reduce cost, and KT does not revive the minion.

(Note that damaging Entities that aren't in Play has no effect, since such Entities do not participate in the Death Creation Step, and Damage Events on Entities not in Play aren't broadcasted, so nothing can trigger on them, even the Entity itself that was damaged.)

Notes:


 * Until a hotfix during Patch 5.0.0.12574 (WotOG patch), killing a minion in Setaside would create a Death Event for it that Cult Master could resolve on.
 * Until Patch 6.0.0.13921 (ONiK patch), Destroying a Hero would instantly kill and send it to the graveyard.

Summon Resolution Step
Related Video for this section: [Hearthstone Science The Summon Resolution Step (Starving Buzzard Bomb, Commanding Shout and more)] (Note that Commanding Shout is no longer an SRS trigger as of Patch 5.0.)

''TODO: Is C'Thun a SRS trigger to catch up on buffs? If so, why does transforming a C'Thun with your Battlecry not work? https://www.reddit.com/r/hearthstone/comments/4go1r6/so_i_was_playing_my_evolving_cthun_and_dragon/ ''

TODO: Lotus Illusionist transforming does trigger Unlicensed Apothecary: https://www.youtube.com/watch?v=7uwy1F54wA0&t=0m57s About time someone tested that ;)

''TODO: When Lady Naz'jar's 'Pearl of the Tides' Hero Power triggers upon ending your turn, if an Unlicensed Apothecary is created, it triggers on all the other minions transforming. https://www.youtube.com/watch?v=oGy7o5KojXo&t=1m41s Therefore there is a Special Summon Resolution Step after the End of Turn Phase. Maybe casting a spell is the ONLY sequence to not have a Special Summon Resolution Step. (Also, ending turn/starting turn is really two different Sequences. Technically, this is because the game's STEP tag changes between them.)''

''TODO: It seems like the Special Summon Resolution Step's timing is related to a second inserted After Play Phase/After Summon Phase, not some 'at the end of the Sequence' mechanism. Is this mechanic new or old? Is it a bug or intended? Should the 'Playing/summoning a minion' section be rewritten to note this, or is it too esoteric to introduce that early? Investigate further and rewrite. https://github.com/HearthSim/hs-bugs/issues/727 https://github.com/HearthSim/hs-bugs/issues/257 ''

When we have previously talked about 3 steps at the end of each outermost Phase, it was an oversimplification. There are actually 5, one of which is the Summon Resolution Step. Here is the real list:


 * 'Previous Phase'
 * Aura Update (Health/Attack) Step
 * Summon Resolution Step
 * Aura Update (Health/Attack) Step
 * Death Creation Step
 * Aura Update (Other) Step
 * 'Next Phase' (a Death Phase if any Death Events were created in the Death Creation Step, otherwise the next named Phase of the Sequence)

Whenever a minion enters play (whether due to being played or summoned), a 'Summon Event' is created, but not resolved. Instead, during the Summon Resolution Step, in order of play, we resolve each Summon Event, Queuing and Resolving triggers.

The following minions and effects are 'Summon Triggers' and trigger in the Summon Resolution Step: Starving Buzzard, Undertaker, One-eyed Cheat, Knight of the Wild, Steward of Darkshire, Maloriak's The Alchemist Hero Power, the Miniature Warfare Tavern Brawl rule (for minions that do not already have 'Miniature' attached). , Cobalt Guardian and Murloc Tidecaller.

Besides, minions resulting from non-spell transformations are counted as 'summoning a minion' and allowed to participate in the Summon Resolution Step, including Faceless Manipulator, Recombobulator, Poultryizer, Lady Naz'jar's Hero Power (from the Boss Battle Royale Tavern Brawl), Thrall, Deathseer's Battlecry and Hero Power, transformation between Sherazin, Corpse Flower and seed , Lotus Illusionist. This might be a bug.

Examples:


 * You play a Starving Buzzard and Druid of the Fang. You didn't play a Beast, just created one via a Transform effect, but as it was a non-spell transformation, Starving Buzzard triggers and draws a card. This also works if you use a Faceless Manipulator and transform it, for example into a Beast (for Starving Buzzard) or something with a Deathrattle (for Undertaker). This also works if you use Tinkmaster Overspark, but not if you use Polymorph.
 * You play a Starving Buzzard, two Knife Jugglers, a second Starving Buzzard then Unleash the Hounds. Each hound summoning triggers the two Knife Jugglers in order of play, then finally when the Spell Text Phase ends, for each hound summoned, the two Starving Buzzards trigger in order of play. Finally, any allied Wild Pyromancers activate. Snake Trap works the same way. Using Savannah Highmane's Deathrattle has a similar result.
 * You play two Undertakers, a Knife Juggler and Dr. Boom. For each Boom Bot summoned, the Knife Juggler triggers, then at the end of the Battlecry Phase, the Undertakers trigger in order of play for each Boom Bot during the "Summon Resolution Step". Finally, the Knife Juggler throws a knife for Dr. Boom's summon.
 * You play a One-eyed Cheat, a Knife Juggler and target your One-eyed Cheat with a Faceless Manipulator. The One-eyed Cheat does not trigger, then the Battlecry turns it into a One-eyed Cheat with no Stealth. The Knife Juggler then triggers in the inserted phase. Finally, during the Summon Resolution Step, the original One-eyed Cheat reacts to the newly summoned pirate, triggering and gaining Stealth.
 * You play two Piloted Shredders and your opponent Flamestrikes. A One-eyed Cheat comes out of both Shredders. At first neither one triggers, but during the "Summon Resolution Step", they react to each other and both stealth.
 * Similar to other Events/Phases, if the minion associated with a Summon Event is no longer in play at the time it is resolved, then nothing queues. For example, if you play Tinkmaster Overspark onto a battlefield of Starving Buzzard and Brann Bronzebeard and Brann is transformed twice, Starving Buzzard only triggers once, on the second Summon Event.

Notes:


 * Before Patch 5.0.0.12574 (WotOG patch), Garrison Commander and Coldarra Drake were a Summon Resolution Step trigger (plus an Inspire trigger).
 * Before Patch 5.0.0.12574 (WotOG patch), Commanding Shout was a Summon Resolution Step trigger. It now seems to be an Aura Update (Health/Attack) trigger.
 * Before Patch 9.0.0.20457, Cobalt Guardian and Murloc Tidecaller were Presummon Triggers. This meant that both the original and the copy would gain Divine Shield/+1 Attack when copied by Molten Reflection and Sudden Genesis.

Quest Reward Step
Quest reward will not be added to your hand immediately you finish your quest, but until the current phase ends. Similar to Summon Resolution Step, Quest Reward Step is also a step between phases, which checks if you have finished your quest and gives you reward. Its timing is before Summon Resolution Step.

Examples:


 * You have Undertaker and Mirror Entity. Your opponent plays Loot Hoarder to finish The Caverns Below, First Mirror Entity copies Loot Hoarder then Crystal Core is added to opponent's hand. Finally, your Undertaker gain +1 Attack.
 * You play Power Word: Shield to finish your Open the Waygate. Time Warp is added to your hand after Djinni of Zephyrs copies the spell. If this makes your hand full, you cannot get the reward.

Timings of Quests and Spellstones
To simplify card texts, Quests and several Spellstones don't indicate accurate timings. Though several effects are described similarly, they may have different timings. A full list is as follows:


 * Druid Quest Jungle Giants is an After Summon Trigger.
 * Hunter Quest The Marsh Queen is an After Play Trigger.
 * Mage Quest Open the Waygate is an After Spell Trigger.
 * Paladin Quest The Last Kaleidosaur is an After Spell Trigger.
 * Priest Quest Awaken the Makers is a After Summon Trigger.
 * Rogue Quest The Caverns Below is an After Play Trigger.
 * Shaman Quest Unite the Murlocs is an After Summon Trigger.
 * Warlock Quest Lakkari Sacrifice is a Discard Trigger.
 * Warrior Quest Fire Plume's Heart is an On Play Trigger.


 * Mage Spellstone Lesser Ruby Spellstone is an After Play Trigger.
 * Priest Spellstone Lesser Diamond Spellstone is an After Spell Trigger.
 * Rogue Spellstone Lesser Onyx Spellstone is an On Play Trigger.

Dominant Player Bug
Related Video for this section: [Hearthstone Science The Dominant Player Bug (Shadow Madness+Power Overwhelming and more)] However, note that the Shadow Madness + Power Overwhelming interaction has been fixed in Patch 5.0; the minion always dies.

''TODO: The Weasel Tunneler interactions need to be re-tested in Patch 8.0, and either modified (if they still display the Dominant Player Bug) or removed (if they do not). See https://github.com/HearthSim/hs-bugs/issues/636 ''

Definition: The Dominant player is the player having PLAYER_ID value = 1. This is decided before, and is unrelated to who goes first/who has the coin. Rule DP1: When triggers (NOT Events) from both players are resolved for a common Event, the Dominant Player's is resolved in order of play first, then the Secondary Player's is resolved in order of play. This is as opposed to all triggers from both players Queuing and resolving in global order of play. Rule DP2: Both player's triggers are queued at the same time - this means if a Dominant Player trigger creates a Secondary Player trigger, it cannot work for the Event resolving now. Rule DP3: If a trigger has priority, the priority only acts in same player's triggers. For example, Redemption owned by the Dominant Player still Resolves before the Secondary Player's triggers for a given Death Event.


 * Dominant Player is called Player 1 in official announcements. So this might not be a bug.
 * It does not affect Events, e.g. the order in which simultaneous Deaths are considered, or the order in which simultaneous damage/healing is considered.
 * A trigger or enchantment is 'controlled' by the Player that caused it to be put into play, and who 'controls' it is what is considered for the Dominant Player Bug. For example, if you play Lucifron, all Corruption enchantments are 'controlled' by you.

Examples:


 * If you and your opponent have Murloc Tidecallers, instead of strictly going by order of play, the dominant player's Murloc Tidecallers go off, then the other's. It has nothing to do with who got the Coin or not, and is consistent per game.
 * If you and your opponent have a Lorewalker Cho, instead of going strictly by order of play, the dominant player 's Lorewalker Cho triggers first. Similarly, if you have a Violet Teacher and your opponent has a Burly Rockjaw Trogg, the dominant player 's on-spell triggers go off first. Similarly, if you have a Gadgetzan Auctioneer and your opponent has a Trade Prince Gallywix and play a spell with 10/10 cards, the dominant player 's on-spell trigger goes first, thus filling the 10th spot in your hand.
 * You play a Kel'Thuzad then your opponent plays Gruul. At the end of his turn, instead of going strictly by order of play, the dominant player's end of turn triggers go first.
 * You play a Flesheating Ghoul then your opponent plays a Flesheating Ghoul. When a Death happens, instead of going strictly by order of play, the dominant player's on-Death triggers go first, per Death (which IS in order of play).


 * The Dominant Player Bug applies to Combat Preparation Phase triggers too. If you attack with a Clumsy minion into traps like Misdirection, the dominant player's trigger goes first, regardless of order of play. Similarly, if both you and your opponent have Mogor the Ogres, all the dominant player's Mogors go off first, then all your Mogors go off.


 * If the Dominant Player plays Redemption and the Secondary Player plays a Flesheating Ghoul, regardless of order of play, when one of the Dominant Player's minion dies while it's not his turn, the Redemption triggers before the Flesheating Ghoul triggers.

Notes:


 * Before Patch 5.0.0.12574 (WotOG patch), Shadow Madness + Power Overwhelming would allow the minion to survive for one more turn if done by the Secondary Player. This was because when the minion changed controllers, the attached Enchantment also changed controllers. As of Patch 5.0, attached Enchantments no longer change controllers. This means it is not removed from the queue, and triggers as normal. As a result, Shadow Madness + Power Overwhelming now always causes the minion to die.
 * Before Patch 2.7.0.9166 (Tavern Brawl patch) the challenger in a friendly match was the Dominant Player always. This seems to no longer be the case, and now seems to be random.
 * Before Naxxramas, the Dominant Player Bug affected the order of Deathrattles resolving. For example, if Sylvanas Windrunner traded into a second Sylvanas, the Dominant Player's Sylvanas's Deathrattle triggered first, instead of using order of play.
 * Before Patch 9.2.0.21517, Secondary Player's triggers are not queued until Dominant Player's triggers are resolved. This cause a Secondary Player's trigger created by Dominant Player's triggers can follow and resolve.

The Order of Battlefield, Hand and Deck Triggers
Related link for this section: https://github.com/HearthSim/hs-bugs/issues/495 

''In Patch 9.2.0.21517, the Quad Queue is reported to have been removed. Need to test, however''

Rule DP4: A clarification of Rule DP1: The same player's triggers in different zones have a fixed order: Dominant Player Play, Dominant Player Hand, Dominant Player Deck, Secondary Player Play, Secondary Player Hand, Secondary Player Deck.

An additional note on Shifter Zerus and Enchantments:

All Enchantments are considered to be in the Play Zone, even if they are attached to a minion in your Hand, Graveyard, Deck or Setaside. The most notable case of this is Shifter Zerus, whose implementation is as follows:
 * An untransformed Shifter Zerus triggers as a Hand Trigger at the Start of Turn Phase to change forms, and attaches the 'Shifting' (OG_123e) Enchantment to himself.
 * The 'Shifting' Enchantment triggers as a Play Trigger at the Start of Turn Phase to change the minion it is attached to. Even though it is an Enchantment to a minion in the Hand, it is itself in Play due to the above rule.

Examples:


 * If you have an Alarm-o-Bot and a Shifter Zerus in your hand, the Shifter Zerus will trigger first if it is already transformed, but the Alarm-o-Bot will trigger first if it is not yet transformed.


 * If you play Curse of Rafaam then your opponent plays Competitive Spirit, despite the play order, Competitive Spirit will trigger first since it exists in the Play Zone.
 * If you have Animated Berserker on board and Patches the Pirate in deck and play a pirate, Animated Berserker will trigger first since if exists in the Play Zone.

Mid-Phase removal and triggers
''TODO: I think this section is slightly over-specific. (Can also consider things like how changing controllers invalidates triggers in the current queue, but may allow them to queue in later queues, like Flesheating Ghoul/Sylvanas vs Dominant Player Bug.) It's actually a pretty fundamental rule and not a bug or likely to change, so maybe it should be integrated into the main Advanced rulebook somehow!''

Rule MPR1: If a minion is removed from play in the middle of a Phase (such as through being returned to the hand, shuffled into the deck or due to Full Zone Instant Removal), all additional triggers attached to it are immediately removed from play and ineligible to trigger. Rule MPR2: Deathrattles are an exception to rule MPR1 - despite being triggers, they can resolve in any zone, including Play, Hand, Graveyard and Deck.


 * Alarm-o-Bot, Anub'ar Ambusher, Malorne, Freezing Trap, Poultryizer (because a mid-Phase Transformation is equivalent), Sylvanas Windrunner (because if the other side of the board is full, the minion will be instantly sent to the Graveyard instead ) and Mimiron's Head (due to the Forced Death Phase before following triggers run) is the full list of effects where this behavior may be observed.

Examples:


 * You play Malorne and cast Ancestral Spirit and Soul of the Forest on it. When Malorne dies, first Malorne is shuffled into your deck, then the additional Deathrattles resolve in play order.
 * You play Anub'arak and Soul of the Forest on Anub'arak. When Anub'arak dies, both Deathrattles will resolve in that order - even though Anub'arak is in the Hand, Deathrattles are eligible to trigger in the Hand zone, so a 2/2 Treant will be summoned onto the board.
 * You play Blessing of Wisdom on a minion and send it to attack into a Freezing Trap. The Freezing Trap triggers first and removes your minion from play before Blessing of Wisdom can draw you a card.
 * You play a Mech, Alarm-o-Bot then Mimiron's Head with only non-Mech minions in your hand. Both players pass. During the Start of Turn Phase, first Alarm-o-Bot goes off and replaces itself with a non-Mech. Mimiron's Head was queued, but since it is no longer eligible it aborts. (Conversely, if Mimiron's Head is played before Alarm-o-Bot, Alarm-o-Bot is removed from play before it can trigger due to the Forced Death Phase. ) Similarly, Poultryizer played before Mimiron's Head may Transform a Mech into a Chicken, and Mimiron's Head will abort as it lacks 3 Mechs now.
 * You play Anub'ar Ambusher then Cult Master. The Anub'ar Ambusher dies. The triggers queued for its death are Anub'ar Deathrattle, Cult Master Trigger. The Deathrattle goes off first and removes the Cult Master from play, so it does not trigger and give you a card.
 * You play Alarm-o-Bot then play Nightmare on it. On your next Start of Turn Phase, the triggers go off in order of play - thus, Alarm-o-Bot enters your hand, then the removed Nightmare does nothing. If you play it again, it is not instantly destroyed.

Notes:


 * Until Patch 5.0.0.12574 (WotOG patch), Deathrattles became immediately ineligible to queue or trigger if the related minion was in the Deck or Setaside Zone. This was fixed to make Malorne + added Deathrattles work as intended. However, if you Feign Death a minion with an original zone-moving Deathrattle, its added Deathrattles still cannot work. This might be a bug.

Avenge, Redemption and Effigy
''TODO: This (and sub-section) needs to be re-written to be a better, more generic explanation of queuing/trigger conditions and placed in the main Advanced rulebook. Ideally instead of a giant list, we would give a general rule for how you determine what somethings' queuing and trigger conditions will be, and then list only exceptions from that. And we should list things like targeted Battlecries as a totally separate concept, since it's not really related at all. Maybe PattuX will have some good ideas?''

Related Video: [Hearthstone Science BONUS #01: Avenge, Redemption and Effigy - Exceptional Triggers ]

Most triggers will Queue when an Event starts being resolved, even if their condition is not true at the time, and then check the condition when the trigger starts being resolved. For example, if you play Cult Master followed by Voidcaller and your opponent kills the Voidcaller, even if you had no Demons in your hand, the Cult Master can draw a Demon and the Voidcaller Deathrattle can put it into play. However, three Triggers - all Secrets - Avenge, Redemption and Effigy all check their Condition twice - both when Queuing and when triggering.


 * Avenge's condition is that the board must be non-empty. For example, if you play Sludge Belcher and Avenge, then your opponent kills the Sludge Belcher, Avenge will not Queue, as at the time of Queuing, there is nothing on the board to buff, even though if it Queued it would have been able to trigger and buff the Slime. Conversely, if you play Anub'ar Ambusher and another minion then Avenge and then your opponent kills the Anub'ar Ambusher, Avenge will Queue because it sees a friendly minion to buff, but at the time of triggering, said friendly minion has been removed from play, and it will not trigger.
 * Redemption and Effigy's condition is that the board must be non-full. For example, if you play Haunted Creeper followed by Anub'ar Ambusher and then either Redemption or Effigy, then your opponent kills both those minions simultaneously, during the Haunted Creeper's Death, Redemption/Effigy will Queue because the board will be non-full, then it will decide not to trigger because the board fills up. Conversely, during the Anub'ar Ambusher's death, Redemption/Effigy will not Queue because the board is full, even though if it did Queue, it could have triggered after the Anub'ar Ambusher's Deathrattle freed up a space.

Additionally, Duplicate has a trigger condition of 'your hand is not full'. It also have a queuing condition of 'your hand is not full'. Gateway Kodo has the same conditions.

Trigger conditions and Queuing conditions
''TODO: There seems to be some kind of new rule that says that a minion can't be bounced to deck and then from deck to hand. Or maybe it's not a moving between zones rule, but a rule about triggers' trigger conditions? Figure out which it is and edit the appropriate section of the two. See https://github.com/HearthSim/hs-bugs/issues/636 ''

Besides the Secrets Avenge, Redemption, Effigy and Duplicate, many other triggers in Hearthstone that have a condition may have the condition as a trigger condition, a queuing condition or both. Sometimes it is difficult to tell which of these three it is without crafting a specific test.

Many of these are listed in the Combat section of the Advanced rulebook. Here are some other examples:


 * Hobgoblin has a triggering condition of 'minion is 1-Attack, or a previous Hobgoblin triggered'.
 * Voidcaller's Deathrattle does not have any condition - it tries to force play a Demon from your hand, and if you lack one it simply does nothing.
 * Chillmaw's Deathrattle has a queuing condition of 'controller is holding a Dragon'. This means if Duplicate triggers before Chillmaw's Deathrattle and adds a Dragon to your hand, the Deathrattle did not queue so nothing happens. Conversely, if a Dancing Swords dies before Chillmaw and draws a Dragon, this is early enough for Chillmaw's Deathrattle to queue and resolve on Chillmaw's Death Event.
 * Alarm-o-Bot's trigger has a queuing and trigger condition of 'controller is holding a minion'. For example, if you have 0 minions and your Nat Pagle (played first) draws a minion at the start of your turn, your Alarm-o-Bot (played second) will not trigger since it never queued.
 * Iron Sensei's trigger has a queuing and trigger condition of 'another friendly Mech exists'. For example, if you have 0 mechs and your Kel'Thuzad (played first) summons one at the end of your turn, your Iron Sensei (played second) will not trigger since it never queued.

(Currently, a comprehensive list of all queuing and trigger conditions in the game does not exist.)

In addition, most Battlecries just have a targeting condition - the condition must be satisfied when you play the minion from your hand and select a target, but it doesn't have to be satisfied again when the Battlecry resolves. This is true for almost every Battlecry in the game - including Gormok the Impaler. (If you play Gormok onto a board of 4 minions and choose a target, but lose one or more of the other minions before the Battlecry resolves, it still deals 4 damage to the target.)

However, several Battlecries work differently - Rend Blackhand, Blackwing Corruptor and Book Wyrmrequire you to be holding a Dragon both when you target the Battlecry and it resolves. Blazecaller and Prince Taldaram work similarly. (Tested by stealing the Battlecry minion before the Battlecry resolves, and the new controller is not holding a Dragon - the Battlecry does nothing.)

In addition, Combo Battlecries - even targeted ones - if stolen before their Battlecry resolves, check the new controller's Combo status. If the new controller played a card on their last turn, Combo will be active. (This is also true for Combo spells played by a stolen Yogg-Saron, Hope's End.

Finally, it should be noted that spells with conditional effects - such as Ice Lance and Demonfire - that do not restrict what they can target, but change the effect based on a property of the target, do not check their conditional effects when targeted, but when resolving. So if the spell is redirected by Spellbender or copied by Djinni of Zephyrs, the condition will be checked at the time of resolution.

When does Overload occur?
''Related video: [Hearthstone Laboratory When Does Overload Occur? (Patch 4.1 post-hotfix)] ''

Because it adds complexity to the Sequences for little predictive benefit (Overload already works rather intuitively), I've split this out into its own section.

The On Play Phase is slightly more complicated than the Sequences suggest. In particular, it looks like this:


 * On Play Phase: All triggers we normally expect here Queue and Resolve (including Counterspell and Unbound Elemental). Then there is an Aura Update, and if not Counterspelled, Overload is incurred. Then Tunnel Troggs Queue and Resolve.

(Also, note that even though there is an Aura Update, there is no Death Creation Step at this timing. There is likely no Summon Resolution Step either, but it is untested.)

This leads to the following consequences:
 * Counterspell prevents Overload, which prevents Tunnel Troggs from triggering, but does not prevent Unbound Elementals from triggering. (After all, you Played an Overload card, you just didn't get Overloaded!)
 * Brann Bronzebeard does not double Overload.
 * Stealing a Battlecry minion pre-Battlecry does not give Overload to the final controller of the minion.
 * During the Servant of Yogg-Saron Tryouts Tavern Brawl, if you play an Overload minion and the spell rolled is Lava Shock, you incur Overload after Lava Shock resolves.
 * Tunnel Trogg is exactly an overload trigger. It can also be affected by Yogg-Saron, Hope's End's overload spells.

There is also one unusual, seemingly contradictory observation - if you silence an Overload minion in the hand and play it, normally the minion is unsilenced before it enters play (giving it its Battlecry back, its Deathrattle back, etc). However, Overload is not incurred.

Where do Minions summoned by Deathrattles spawn?
When only one minion dies, the position of its summoned minions is intuitive. However, as soon as multiple minions die at once, the results may defy expectations, like a Nerubian appearing between two Spectral Spiders. Here are the rules Hearthstone uses:


 * 1) During the Death Creation Step, all minions that are mortally wounded or 'pending destroy' have their Death Events created in play order.
 * 2) When a Death Event is created, the minion is removed from play and moved to the Graveyard, and it remembers its board position, counted from left to right. (Note that that the n-th played minion ignores the first to (n-1)-th played minions when counting it's new position, because they already left play.)
 * 3) During the subsequent Death Phase, their Death Events are resolved in play order. Any minions summoned by Deathrattles triggering on the Death Event are summoned in the board position the Death Event remembered from when it was created. (Note that previous triggers changing the board state is not taken into account - the remembered board position is used without modification.)

Examples of these rules in action can be observed by studying the video Hearthstone - Dreadsteed vs Knife Juggler.

Example: 3:05


 * 1) The 2nd and 7th Dreadsteed die. The 7th was just spawned, so the 2nd was played first.
 * 2) The 2nd dies and calculates its Death Event position: 2.
 * 3) The previously 7th minion dies, but as the 2nd Dreadsteed already died, it calculates the new board position, ignoring the 2nd one which already died, as 6.
 * 4) Now they spawn in the same order: 2nd first, then 6th.

Another example is in this video Hearthstone Deathrattle Chevron Puzzle Solution which is the solution to this puzzle Flamestrike Deathrattle Chevron.


 * 1) The Savannah Highmane is played first, followed by the Haunted Creeper and finally the Harvest Golem.
 * 2) Two additional minions are played afterwards to control the board position during death events of the Savannah Highmane, Haunted Creeper and Harvest Golem.
 * 3) A Flamestrike is played, killing all minions.
 * 4) The Savannah Highmane dies at position 0 (0-indexed) and is removed.
 * 5) The Haunted Creeper dies at position 1. This is because after the Savannah Highmane has been removed, the left-most Elven Archer occupies position 0 and the Haunted Creeper occupies position 1. The Haunted Creeper is then removed.
 * 6) The Harvest Golem dies at position 2 as positions 0 and 1 are occupied by Elven Archers.
 * 7) The two Elven Archers die and are removed.
 * 8) The Savannah Highmane's deathrattle triggers first as it was the earliest played minion. The two Hyenas spawn at position 0.
 * 9) The Haunted Creeper's deathrattle triggers next and the two Spectral Spiders spawn at position 1. This happens to be between the two Hyenas. Resulting in the configuration Hyena, Spectral Spider, Spectral Spider, Hyena.
 * 10) Finally, the Harvest Golem's deathrattle triggers and a Damaged Golem spawns at position 2, which is in between the two Spectral Spiders.

Notes:


 * Feign Death and similar effects summon minions at the right side of the board, not the minion's position.
 * These deathrattles also summon minions at the right side: Stalagg, Feugen, Soul of the Forest, Meat Wagon, Giant Anaconda and Deathwing, Dragonlord.

Controllers of Enchantments and Minions
Rule CEM1: Enchantments have a CONTROLLER tag equal to the player who put them into play (such as with a Battlecry, Spell or trigger). This can be different from the CONTROLLER tag of the Entity (usually Minion) they are attached to. Its current CONTROLLER value is used whenever an Enchantent needs to know one of the following things: Rule CEM1b: Which player's Start of Turn Phase to trigger in (Conceal, Finicky Cloakfield, Master of Disguise, Corruption, Nightmare) Rule CEM1c: Whether to queue in the Dominant Player's queue or the Secondary Player's queue (all Enchantments with triggers). Rule CEM1d: Which player's battlefield to look for an Auchenai Soulpriest/Embrace the Shadow effect in (Power Word: Glory). Rule CEM2: However, the Enchantment's CONTROLLER tag is NOT used for the following: Rule CEM2a: Which Hero to heal/which player to draw a card for (Blessing of Wisdom, Power Word: Glory) Rule CEM2b: For Enchantments that add Deathrattles, who gets the effect and whether to queue (and also whether it can resolve at resolution time) in the Dominant Player's queue or the Secondary Player's queue. For both of these things, the minion's CONTROLLER is always used instead. (Ancestral Spirit, Explorer's Hat, Soul of the Forest) Rule CEM2c: For Enchantments that add Spell Damage +1 (like Velen's Chosen, Ancient Mage and Dalaran Aspirant, the minion they are attached to always gives the effect to the minion's controller, regardless of who originally cast it. Rule CEM3: Whenever a minion changes CONTROLLERs, all attached enchantments do not change CONTROLLERs - they are still considered to be controlled by the original caster.

Examples:


 * If Player A plays Nightmare on a minion, no matter how many times it changes controllers, the Enchantment it creates will trigger to destroy the minion in Player A's next Start of Turn Phase.
 * If Player A plays Velen's Chosen on a minion, it will always give Spell Damage +1 to the minion's current controller, not the original caster.
 * If Player A plays Power Word: Glory on a minion belonging to either player, when the Enchantment it creates triggers, it checks if Player A has an Auchenai Soulpriest effect, no matter how many times the attached minion changes controllers.
 * If the Secondary Player owns a Webspinner and the Dominant Player casts Explorer's Hat on it, regardless of whether it dies or Feign Death is casted, the Webspinner Deathrattle will resolve before the Explorer's Hat, because the Explorer's Hat uses the minion's controller, not its own controller, to decide what to do.

Notes:
 * Prior to Patch 5.0.0.12574 (WotOG patch), whenever a minion changed CONTROLLERs, attached Enchantments also changed CONTROLLERs. This causes some unusual interactions with Nightmare and Power Word: Glory.

Huge Enchantment Rounding Bug
TODO: This is fixed in 8.2 for Divine Spirit: https://github.com/HearthSim/hs-bugs/issues/104#issuecomment-306006806 How about for other Enchantments?

Some Enchantments, when applied to a minion, have to remember a value to directly set Health/Attack to, or a value to increment Health by. They do this by assigning values to two tags: TAG_SCRIPT_DATA_NUM_1 and TAG_SCRIPT_DATA_NUM_2. Such Enchantments all have a rounding bug, because they calculate the value of these tags erroneously using float precision, rather than 32 bit integer (or better) precision. Due to this, they only have ~24 bits of precision available, and rounding errors will start to appear after dealing with Health/Attack values higher than about 16777216. Integers that require more bits of precision than this will be rounded (up or down, but ties broken by rounding down) to the nearest valid float, destroying information contained in the lowest bits.

C++ sample code that simulates the rounding bug is available here: http://pastebin.com/E7r8mQtX

Examples:


 * Divine Spirit is coded to create a Health increase Enchantment equal to the minion's current Health. Due to the rounding bug, if you apply it to a minion with slightly more than a power of 2 current Health, the amount of Health added will be rounded down.
 * Crazed Alchemist and other swap effects remember the values of current Health and Attack at the time of application, and create Direct Set effects that set Attack and Health to those values. Due to the rounding bug, applying this to a minion with slightly less than 2^31-1 current Health will attempt to directly set its Attack to 2^31 (which is clamped to 0 by Hearthstone).
 * Inner Fire Direct Sets a minion's Attack equal to its current Health. Due to the rounding bug, applying this to a minion with slightly more than a power of 2 current Health will round its Attack down.

Notes:


 * Attack doubling Enchantments like Gahz'rilla and Blessed Champion do not memorize at the time of application an amount of Attack to add, but dynamically double the attack whenever it is recalculated. Due to this, they do not suffer the rounding bug.

Unusual Aura Update (Health/Attack) timings
''TODO: This section is a WIP. Refer to https://github.com/HearthSim/hs-bugs/issues/325. No one has re-tested any of this in Patch 5.0 BTW.''

1) Aura Update (Health/Attack) sometimes doesn't run.


 * The rule seems to be that if no Entity was created, moved or silenced since the last time Aura Update (Health/Attack) ran, it is skipped. (On the other hand, sometimes it seems to run anyway - perhaps there is one guaranteed AU(H/A) near the start and end of each Sequence, for example?) More information is here: https://www.youtube.com/watch?v=Yh3yvKPZ-G8

Yet, for example:

[10:19]  no on-play/srs/pre summon triggers result in 2 updates before battlecry

Why is this, and what are their timings?

2) There are many places where Aura Update (Health/Attack) runs, that are unexpected:


 * Once before and after each Summon Resolution Step following each outermost Phase (Summon Resolution Step), but only AFTER the Summon Resolution Step before a Forced Death Phase Forced Death Phase.
 * Once when Overload is incurred (When does Overload occur?). It is currently unknown if this Aura Update always happens, or only if Overload is incurred.
 * It seems to happen when Imperial Favor is detached, and probably also when other Mana Cost Enchantments trigger to detach, such as Kirin Tor Mage, Preparation, Dragon Consort, Fencing Coach, etc.
 * It seems to happen under an unknown set of conditions when adjacent Auras, like Flametongue Totem, change what minions are next to them. See User_talk:Patashu
 * Between the two Battlecries if Brann Bronzebeard is in play. (We haven't tested if Brann + Discover Battlecry adds any extra Aura Update (Health/Attack) Steps anywhere. See Delayed Discoveries)

3) It's possible to look for Aura Update (Health/Attack) timings by attaching a Health/Attack buffing Enchantment to a minion outside of play.

Every Aura Update (Health/Attack), the Enchantment is considered to be in play and thus buffs the minion's Health/Attack, but the minion wasn't in play to reduce its own Health/Attack to base stats before the recalculation occurred, meaning that every Aura Update (Health/Attack) the minion's Health/Attack will rise without bound.

Ways to do this include Faceless + Brann on an Enchanted minion, minion leaving play before Battlecry/Spell applies an Enchantment, etc.

What actually ignores Mortally Wounded?
''TODO 1: We tested only random damage, random destroy, Freezing Trap and Grim Patron. Everything else on 'ignores mortally wounded' should be tested with pending destroy minions. https://www.youtube.com/watch?v=jcniWFdCBKY ''

''TODO 2: Ragnaros, Lightlord heals mortally wounded. https://www.reddit.com/r/hearthstone/comments/4gkyva/ragnaros_lightlord_play_is_it_a_glitch/ and pending destroy http://us.battle.net/hearthstone/en/forum/topic/20744094286 So we need to re-test Lightwell, which hasn't been re-tested since Patch 4.1: https://www.youtube.com/watch?v=v2b_O48kSKA ''

Rule 5 talks about what effects ignore mortally wounded (0 or less Health)/pending destroy (hit by a Destroy effect this Phase) Characters, and what effects include them. (Note that they are in play, take up space, and can still trigger - so it's a matter of what effects are coded to ignore them, and what effects are coded to include them.) But it is an informal oversimplification. Here is the real list:


 * Ignores mortally wounded/pending destroy: Random steal effects (Sylvanas Windrunner ), Random/conditional bounce effects (Freezing Trap, Anub'ar Ambusher ), random damage (Knife Juggler, Arcane Missiles), random destroy effects (Stampeding Kodo, Void Crusher), survival checks (Grim Patron)  , Misdirection  , Mirror Entity, Snipe, Repentance, Potion of Polymorph and Sacred Trial


 * Includes mortally wounded/pending destroy: Area of effect damage/healing (Explosive Sheep, Baron Geddon, Healing Totem , Tree of Life, Holy Nova ), random healing (Ragnaros, Lightlord ) buffs/debuffs (Avenge , Anubisath Sentinel , Dark Cultist, Maloriak , Powermace , Competitive Spirit ), Hidden Cache and Frozen Clone


 * Unknown: Forgetful effects (Mogor the Ogre, Ogre Brute, Ogre Warmaul)


 * Note: Noble Sacrifice triggers even if the attacker is mortally wounded or removed from play because it has a side-effect it can still do.

As you can see, it's not especially clear! If I can think of a way to condense this down into something catchy, it will become the new Rule 5.

Trigger Re-entrancy Exploration
''TODO: This hasn't been tested in Patch 5.0 and thus may be outdated. It is also currently unknown how this generalizes to triggers in general, only a few cases have been tested.''

We know in general that Hearthstone does a greedy, depth-first search with regards to resolving events and triggers. But it seems that if a trigger occurs inside of itself, the tree is re-written in some way that post-pones the new firing of the trigger until the old firing of the trigger resolves, but all the correct number of triggers still eventually occur.

This can be seen in two videos:
 * https://www.youtube.com/watch?v=rdx5WpFuRYM [Hearthstone Science] 13 Flame Leviathans in One Turn
 * https://www.youtube.com/watch?v=4fvN2S1bLOA [Hearthstone Science] Floating Watcher has higher priority than Queen of Pain (the title is, of course, a misnomer now that we know that it's because of the tree-rewriting, not something innate to Floating Watcher)

But this only seems to be true for triggers like Acolyte of Pain and Floating Watcher/Queen of Pain. For Knife Juggler, something completely different happens: If a Knife Juggler would trigger while it is in the middle of triggering, the new trigger is lost.

This can be seen in Hunter of the North's video: https://www.youtube.com/watch?v=oNaN4w_TjHc&t=1m50s Explanation of the missing juggle: https://gist.github.com/Patashu/ac7ec3e030e1254c904e

Currently we do not know what rule distinguishes triggers like Knife Juggler from triggers like Acolyte of Pain.

---

Hunter of the North gets a more complicated version of Flame Leviathans + Acolytes of Pain in Patch 3.1. Notice how all of the Acolytes of Pain trigger once, then the last one triggers many times - and backwards in order of play, they each trigger many times before letting those older than them trigger once each. https://www.youtube.com/watch?v=DowBB0GhGnA

In total, 16 flame leviathans run their on-draw effect, the Rogue has four Acolytes and the Priest has six Acolytes.

Rogue: draws 6 flame leviathans then takes fatigue 3-61 for a total of 16*4+1 draws

Priest: draws 10 flame leviathans, mills 2 flame leviathans then takes fatigue 6-89 for a total of 16*6 draws

So the correct amount of Acolyte triggers happen, but the order is unusual.

For example:

Acolyte #1 triggers once at the start, then 15 times just before Acolytes #2-10 trigger once each.

Acolyte #2 triggers once after Acolyte #1's first trigger, then at the end 14 times just before Acolytes #3-10 trigger once each, then one time after Acolyte #1 triggers 15 times.

Acolyte #3 triggers once after Acolyte #2's first trigger, then at the end 13 times just before Acolytes #4-10 trigger once each, then one time after Acolyte #2 triggers 14 times, then one time after Acolyte #2 triggers after Acolyte #1 triggers 15 times

...

Acolyte #10 triggers once then 6 times after Acolyte #9's first trigger, then once after Acolyte #9 triggers 7 times, then once after Acolyte #8 triggers 8 times -> Acolyte #9 triggers 1 time, then... etc.

So in total the triggers are ordered like the following (1 is Acolyte #1, 0 is Acolyte #10):

1234567890 000000 99999990 8888888890 777777777890 66666666667890 5555555555567890 444444444444567890 33333333333334567890 2222222222222234567890 111111111111111234567890

For a total of 16*10 = 160 triggers.

Another data points:
 * If you have a Daring Reporter and your opponent draws many Ambush! cards in a row, all of the Ambush! cards trigger in a row, then the Daring Reporter triggers once for each card drawn.
 * There are a friendly Howlfiend, an enemy Howlfiend, an enemy Acolyte of Pain and a friendly Acolyte of Pain in the order of play (denoted as FH, EH, EA and FA). There are lots of Flame Leviathans in both decks, and your opponent draws one in Draw a Card Phase. First are FH, EH, EA. Then it loops in FH, EH, FA order until your first Fatigue. Next it loops in FH, EH, EA order until your opponent's first Fatigue. Now both player have lots of Fatigue not resolved, but the game ends in a draw after your opponent's second Fatigue.
 * You play 2 Shadowboxers (denoted as 1 and 2 in play order) and give 1 Elixir of Life(The healing of it is denoted as 3). Then you heal your hero. First are 1,3,2,2. Then it loops in 1,3 order until your hero is fully healed. Finally 2 triggers multiple times.

<!--== Rule Summary ==

Definitions
Definition: Player Actions are actions a player chooses to take on their turn while nothing is happening, such as attacking, playing a card, using your Hero Power and ending your turn. Definition: A Sequence is what begins when a Player Action is taken. A Sequence consists of one or more Phases, that are resolved in order. Definition: Phases are surrounding blocks created whenever one or more triggers/Events are raised. When the outermost Phase resolves, Hearthstone will run several Steps, including processing Deaths and updating Auras. Definition: An Event is any change in the game state. For example: Damage Event, Heal Event, Death Event, etc. (Additionally, all Phases have an associated Event(s).) Definition: A Trigger is something that reacts to an Event, i.e. triggered effects, Secrets and Deathrattles. Definition: Resolving means playing out all related consequences, one at a time. Definition: A Queue is a sequential container where multiple simultaneous triggers or Events are held. Definition: The Dominant player is the player having PLAYER_ID value = 1. This is decided before, and is unrelated to who goes first/who has the coin.

Sequences, Phases, Queues, Resolution
Rule 1a: A Phase, trigger or Event is only resolved when all of its consequences are resolved. Rule 1b: When resolving simultaneous events, Hearthstone must resolve one event before it begins resolving the next. Rule 1c: Death and Auras are not checked during the standard resolution of Events. Rule 2a: When we start to resolve a Phase or Event, A Queue is created and filled with all triggers that can respond, in order of play. Rule 2b: If multiple events are considered simultaneously (such as damage, healing, Deaths or 'return to hand' effects) they are Queued by order of play, then for each, triggers are Queued by order of play (as per Rule 2a). Rule 2c: A Queue becomes immutable once Hearthstone starts to resolve the first entry in it. No new entries can be added to the Queue after this point. Rule 3: Once a Phase begins, nested Phases with their own Queues may start and end inside of it, but only the outermost Phase ending initiates the Death Creation Step. Rule 4a: After the outermost Phase ends, Hearthstone does an Aura Update (Health/Attack), then does the Death Creation Step (Looks for all mortally wounded (0 or less Health)/pending destroy (hit with a destroy effect) Entities and kills them, removing them from play simultaneously), then does an Aura Update (Other). Entities that have been removed from play cannot trigger, be triggered, or emit auras, and do not take up space. Rule 4b: Besides, whenever a minion is summoned (but not played), Hearthstone updates both kinds of Auras. Rule 4c: The full list of Auras that are known to update in Aura Update (Other) (excluding Solo Adventure-only content) is as follows: Baron Rivendare, Auchenai Soulpriest, Brann Bronzebeard, Mal'Ganis's Immune effect, Prophet Velen, Violet Illusionist, Drakkari Enchanter, The Four Horsemen (Hero Power). Rule 4d: Enchantments apply and modify Health/Attack/Mana costs the moment they are attached. However, during Aura Update (Health/Attack), the Enchantment List is re-processed and Health/Attack Auras, having a priority later than Health/Attack Enchantments, will be moved to the end of the Enchantment List during this timing. (However, Mana Cost Auras have no special priority compared to Mana Cost Enchantments.) Rule 5: While characters cannot be killed in the middle of a Phase, 'negative' (damaging/destroying/hindering/misdirecting) triggers ignore mortally wounded and pending destroy characters. Also, Secrets abort if their specific target is mortally wounded, pending destroy or they otherwise cannot meaningfully trigger. However, 'beneficial' (healing/buffing) triggers count mortally wounded, and AoE effects count mortally wounded. Rule 5b: For the purposes of 'if it survives'/'if that kills it' effects, mortally wounded and pending destroy Characters are considered to not have survived/to have been killed, even though they are (for now) still in play. Rule 6: Subsequent Phases of a Sequence will not run if a subject is required but is no longer in play. However, this is the only requirement - If the target of the action has some requirements beyond that, the requirements are not re-checked. Rule 7: If one or more Deaths happened after the outermost Phase ended, a new Phase (called a “Death Phase”) begins, where Deaths are Queued in order of play. For each Death, all Death Event triggers (Deathrattles, on-Death Secrets and on-Death triggered effects) are Queued and resolved in order of play. When this is complete, the Death has been resolved. Rule 8: A Death Phase can have yet another Death Phase after it. This process repeats forever until no new Deaths occur, and we can finally move on to the next intended Phase in the Sequence. Rule 9: Finally when the Sequence ends and the player gets control again, Hearthstone checks if the game has ended in a Win, Loss or Draw. Rule 10: Minions and effects have no memory of earlier board state. The moment an event takes place the board state is updated. Whenever a Queue is populated or an effect resolved (or continued), the most up to date board state is used. Rule 10b: Triggered effects with a condition do not check their condition until the moment they queue or the moment they trigger (or sometimes both). Again, they have no memory of prior game states, and their condition succeeds or fails based on the current game state.

Health
Rule H1: Any time a minion's maximum Health is increased, its current Health is increased by the same amount. Rule H2: However, when a minion's maximum Health is reduced, its current Health is only reduced if it exceeds the new maximum.

Enchantments
Rule E1: If a minion has multiple enchantments, they are applied to the minion in order of play. Rule E2: When a temporary enchantment is removed from the middle of the enchantment list, the minion's state is recalculated from scratch. Rule E3: When a minion is Enraged, it creates an enchantment with that effect. If it later becomes un-Enraged (losing the enchantment) and then re-Enraged, it creates a new enchantment, rather than re-creating the old one with its old order of play.

Zones
Rule Z0: If Hearthstone would generate a new Entity in a Zone but the limit has been reached, instead nothing happens. Rule Z1: When an Entity tries to move from one Zone to another, it first checks if the destination is full. If it is, it instead dies and moves to the Graveyard Zone. Rule Z1b: If an Entity tries to move from a Zone to the Zone it's already in, do not apply Rule Z1 (such as steal effects on a minion you already control, or bounce effects on a minion already in your hand). However, other effects of the zone change still happen (such as gaining summoning sickness). Rule Z2: If multiple Entities are moved from one Zone to another simultaneously, they check and move themselves in order of play, and thus newest minions are the ones that get Destroyed if there is insufficient room. Rule Z3: If Kezan Mystic tries to steal a Secret but none can be stolen (because your Secret Zone is full or you already have a copy of all enemy Secrets), a random Secret is destroyed and revealed. Rule Z4: If you would draw a card but have no room for it, its side-effects of drawing (such as Flame Leviathan's or Burrowing Mine's) do not trigger, because it never entered your hand. Rule Z5: When an Entity moves from one zone to another, the minion's tags (such as Damage, Divine Shield and pending destroy) are reset to a default state. In addition, attached Enchantments may be detached. The rules are as follows: Rule Z5a: Play Zone to any other Zone: All Enchantments detached. Rule Z5b: Hand Zone to Play Zone: Enchantments are NOT detached. (However, Mana cost related Enchantments will trigger to detach in the On Play Phase.) Rule Z5c: Deck Zone to any other Zone: Enchantments are NOT detached.

Mana Crystals and mana costs
Rule M1: Your current mana is capped at 10 but has no lower limit. Negative current mana is displayed as 0. Rule M2: Your maximum mana (number of Mana Crystals) is always at most 10 and at least 0. Rule M3: Your current/pending Overloaded Mana Crystals has no upper limit. Rule M4: Gaining or losing maximum mana has no effect on your pending/current Overload. Rule M5: The mana cost of a card has no lower limit. Negative mana costs are displayed as, and use, 0, but help to counteract mana cost increases. Rule M6: When multiple effects change the cost of a card or your Hero Power, they are applied in order of play (Auras and Enchantments having no special priority). One exception is Summoning Portal's aura, which has a very early Priority that makes it considered before ALL other effects. Besides, cards that apply a Mana Cost Aura (Molten Giant, Volcanic Drake, Dread Corsair, etc) have a latest priority. Rule M7: When an effect refers to the cost of casting a spell (such as Summoning Stone or Gazlowe), it means the amount of mana you paid to cast it, not the base mana cost.

Drawing a Card
Rule DC1: When you draw a card, if you have room, it enters your hand and is immediately resolved (according to the below rules). When multiple cards would be drawn simultaneously, the number of cards that would be drawn is calculated, then each one is drawn and resolved in some sequential order. (For example, Coldlight Oracle always draws two cards for its controller first.) Rule DC2: Some effects (Chromaggus, Shadowfiend) trigger when a card is drawn. They trigger in order of play. Then, the card may have an effect when drawn (Sea Reaver, Flame Leviathan, Ambush!, Burrowing Mine, Fatigue, etc). This effect resolves now. When this is complete, the card draw has been resolved. Rule DC3: Some effects (Gnomish Experimenter, Holy Wrath, Far Sight, Call Pet) draw a card, then do something with that card. These effects wait for the card draw to resolve before continuing. Holy Wrath in particular does not require the card to successfully enter your hand. Rule DC4: A card is only considered drawn if it moves from the top of your deck to your hand. If your hand is full, the card is not drawn, nor is it discarded (such as for Tiny Knight of Evil or Fist of Jaraxxus), it just goes to the Graveyard. Rule DC5: An effect is not considered to have drawn a card if it was drawn indirectly (for example, if Varian Wrynn draws Ambush! which itself draws a minion, the minion is not put in play).

Damage and Healing
Rule DH1: When an area of effect Damage or Healing effect happens, all of the Damage/Healing Events are created in play order, then all of the Damage/Healing Events are resolved (queuing and resolving triggers) in play order. Rule DH2a: When a Damage/Healing Event is created: Apply Auchenai Soulpriest. Then apply Spell Damage/Fallen Hero/Arcane Amplifiers. Then apply Prophet Velens. If the target is Immune or the Damage Event's proposed damage is 0, the Damage Event is prevented. Then if the target has Divine Shield, the Divine Shield is removed and the Damage Event's proposed damage is reduced to 0. Then queue and resolve Predamage triggers (see Rule DH7). Then the Character's current Health+Armor is reduced by the Damage Event's proposed damage. (If the target is affected by Commanding Shout, its current Health is prevented from dropping below 1.) Rule DH2b: When a Damage/Healing Event is resolved: If it was prevented, or if it did not change the Character's current Health+Armor total (including due to Divine Shield and Commanding Shout), it will not run any triggers. Otherwise, they queue and resolve in play order. Rule DH3: Some Damage effects sound like they should be area of effect (and therefore create all Damage Events before any of them resolve), but actually resolve each Damage Event as soon as it is created in play order. These are: Lightning Storm, Elemental Destruction, Dark Iron Skulker, Lightbomb. However, these effects still figure out the set of minions they will damage before beginning to damage anything. Rule DH4: Two-step spells (such as Light of the Naaru, Mortal Coil, Bane of Doom, Slam, Bash, Bouncing Blade) that create one or more Damage/Healing Events before then querying the target's condition, must resolve the Damage Event BEFORE they query the target's condition. Rule DH4b: Some other Two-step spells exist: Holy Nova creates and Resolves all Damage Events, then creates and resolves all Healing Events (even if the Healing Events are turned into Damage Events by Auchenai Soulpriest). Blizzard creates and resolves all Damage events, then freezes all enemy minions (even undamaged ones). Cone of Cold creates and resolves all Damage events, then freezes the minions it damaged. Rule DH4c: One spell, Imp-losion, deals damage then queries how much damage was dealt. Divine Shield sets the damage dealt to 0 and Immune prevents the damage, however Commanding Shout does not modify how much damage was considered to be dealt - therefore the normal number of Imps will be summoned. Rule DH5: Some effects create Damage Events out of order of play, likely due to a bug - and therefore they also resolve out of order of play. Swipe damages the target Character, then all other enemy Characters in reverse play order, then resolves all Damage Events. Explosive Shot, Cone of Cold and Powershot damages minions in the order center, left, right. Rule DH6: When a minion is the source of a Damage Event, even if the Damage Event's proposed damage is 0, it loses Stealth. (If the Damage Event is prevented, it does not lose Stealth.)

Predamage Triggers
Rule DH7: Just before a Damage Event is created, Predamage triggers will queue and resolve in play order. They will stop triggering if the Damage Event is prevented, as there is nothing to do. The full list of Predamage triggers is Bolf Ramshield, Ice Block, Animated Armor. Additionally, Animated Armor has an early priority. Rule DH7b: Bolf Ramshield's effect is to prevent the Damage Event, then create a Damage Event who's source and target is Bolf Ramshield, and who's proposed damage is the same as the original Damage Event's. Rule DH7c: Animated Armor's effect is to lower the Damage Event's proposed damage to 1. Rule DH7d: Ice Block's effect is, if the Damage Event's proposed damage is currently greater than or equal to your Hero's current Health, to prevent the Damage Event and create an Enchantment attached to your Hero which says "Become Immune until the turn ends."

Cursed Blade
Rule DH8: Cursed Blade's effect is to double the proposed damage of Damage Events targeting your Hero (whenever queried by a Predamage trigger or when your Hero takes the damage).

Death Event Cache
Rule DEC1: Hearthstone keeps track of every Death Event that has been created this game in the Death Event Cache. It remembers the Entity ID that died, its controller when it died, and what turn it died on. Rule DEC2: If the same minion dies more than once (for example if it's the same Malorne), each Death Event is added to the Death Event Cache separately. Rule DEC3: Cards that check if a minion has died this turn/this game (Feugen, Stalagg) and cards that resurrect minions that died this turn/this game (Resurrect, Kel'Thuzad, N'Zoth, the Corruptor, Anyfin Can Happen, Doomcaller) do not check the Graveyard Zone. They check the Death Event Cache. Rule DEC4: Resurrect effects summon new, fresh copies of minions based on the Death Event(s) they select, and do not remove the Death Event from the Death Event Cache. Except for Kel'Thuzad who uses order of play, Death Events are selected in random order.

Dominant Player Bug
Rule DP1: When triggers (NOT Events) from both players Queue for a common Event, there are actually two Queues - First, the Dominant Player's Queue is populated and resolved in order of play, then the Secondary Player's Queue is populated and resolved in order of play. This is as opposed to all triggers from both players Queuing and resolving in global order of play. Collectively we call this the Split Queue. Rule DP2: When a trigger would resolve, if its controller is not correct for the queue its in (probably because it changed between queuing and resolving), it does not resolve. However, it can now be added to Queues belonging to the new player. This is true even if the trigger does not care who its controller is (such as Flesheating Ghoul). (Note that Enchantments do not change controllers when the minion they are attached to changes controllers as of Patch 5.0.0.12574 (WotOG patch), but added Deathrattles use the controller of the related minion, which CAN change). Rule DP3: If a trigger has priority, the priority only acts within the Queue it's in. For example, Redemption owned by the Dominant Player still Queues and Resolves before the Secondary Player's Queue begins for a given Death Event.

The Quad Queue Model
Rule DP4: A clarification of Rule DP1: There are actually four Queues, not two, in the following order: Dominant Player Play, Dominant Player Hand, Secondary Player Play, Secondary Player Hand. Collectively we call this the Quad Queue.

Mid-Phase removal and triggers
Rule MPR1: If a minion is removed from play in the middle of a Phase (such as through being returned to the hand, shuffled into the deck or due to Full Zone Instant Removal), all additional triggers attached to it are immediately removed from play and ineligible to trigger. Rule MPR2: Deathrattles are an exception to rule MPR1 - despite being triggers, they can resolve in any zone, including Play, Hand, Graveyard and Deck.

Controllers of Enchantments and Minions
Rule CEM1: Enchantments have a CONTROLLER tag equal to the player who put them into play (such as with a Battlecry, Spell or trigger). This can be different from the CONTROLLER tag of the Entity (usually Minion) they are attached to. Its current CONTROLLER value is used whenever an Enchantent needs to know one of the following things: Rule CEM1b: Which player's Start of Turn Phase to trigger in (Conceal, Finicky Cloakfield, Master of Disguise, Corruption, Nightmare) Rule CEM1c: Whether to queue in the Dominant Player's queue or the Secondary Player's queue (all Enchantments with triggers). Rule CEM1d: Which player's battlefield to look for an Auchenai Soulpriest/Embrace the Shadow effect in (Power Word: Glory). Rule CEM2: However, the Enchantment's CONTROLLER tag is NOT used for the following: Rule CEM2a: Which Hero to heal/which player to draw a card for (Blessing of Wisdom, Power Word: Glory) Rule CEM2b: For Enchantments that add Deathrattles, who gets the effect and whether to queue (and also whether it can resolve at resolution time) in the Dominant Player's queue or the Secondary Player's queue. For both of these things, the minion's CONTROLLER is always used instead. (Ancestral Spirit, Explorer's Hat, Soul of the Forest) Rule CEM2c: For Enchantments that add Spell Damage +1 (like Velen's Chosen, Ancient Mage and Dalaran Aspirant, the minion they are attached to always gives the effect to the minion's controller, regardless of who originally cast it. Rule CEM3: Whenever a minion changes CONTROLLERs, all attached enchantments do not change CONTROLLERs - they are still considered to be controlled by the original caster.   -->

Rule changes

 * AoE damage that hits all minions now ignores mortally wounded minions, becoming inconsistent with AoE damage that hits all characters hitting mortally wounded minions.
 * AoE damage that hits all characters now hits mortally wounded minions, consistent with AoE damage that hits all minions.
 * Area of effect healing effects now affect all targets simultaneously, rather than one at a time. Related triggers will still activate one at a time.
 * Secrets can now only activate on your opponent's turn.
 * Unknown alpha patch: Turn time reduced from 90 to 75 seconds.

Why isn't there an official rulebook?
From the start, Hearthstone was designed to be quick and easy to learn, with new players able to have grasped the basics by the end of the tutorial. The game is often compared with card games such as Magic: The Gathering, featuring highly complex and "extremely detailed" rulesets, with official comprehensive rulebooks which are regularly updated and consulted during tournaments. In contrast, Hearthstone 's simple rules allow new players to pick up the game in minutes, with a minimally challenging learning curve. This makes the game far more accessible, increasing the appeal of the game and allowing it reach many players who might not wish to invest the time and effort in learning a more complex ruleset.

However, while the basic operations of the game are usually without uncertainty, there are still times when the precise results of actions can be unclear in advance, especially when several advanced effects are in play. For this reason, some players have called for an official rulebook to be included in the game.

The main reason developers have given for the lack of an official rulebook is the desire to keep the game's rules essentially simple, and the game itself accessible. Hearthstone is intended to be playable without consulting a list of rules, and the addition of a rulebook would be contrary to this design goal, as well as potentially encouraging the game to develop in increasingly complex ways. Game designers such as Ben Brode have stated a desire to keep the game simple and accessible enough to be understood without such resources.

Critically, the lack of a rulebook is made viable by the digital nature of the game, with the system itself instructing players of many of the basic rules of the game, such as highlighting all permitted moves in a turn, and preventing players from taking illegal actions. Tooltips for keywords further assist players in learning and remembering the basic rules. In most intermediate Hearthstone play, there is also relatively little uncertainty over the operation of the basic rules, obviating most of the need for a rulebook. This approach helps to ease new players into the game; Basic cards are designed to be simpler than cards of other sets for this reason.

How does the Hearthstone team keep track of all the rules in Hearthstone?
In a public AMA on August 11, 2020, Software Engineer syah_hs explained how the Hearthstone team manages to keep track of all the rules in Hearthstone and how the game rules are always verified with unit tests to make sure that they work properly with new additions to the game:


 * There are several human-language documents. They range from step-by-step walkthroughs of interactions to collections of "tribal knowledge" to pass down to future generations. None of this is really fit for public consumption. I think the most important part of our documentation is our collection of unit tests. These tests validate that specific card interactions work and that those interactions don't change as we make other changes to provide new functionality or improve processes.


 * When we're presented with new card ideas from the design team, a common question that comes up is "How would this effect work in this situation?" One thing I love about our design team is that the response to that question is usually "How would you expect it to work?" This helps us derive the right wording for a card or even to determine if an effect is too complex early on.


 * When we're thinking about the right way to implement a card we rely heavily on what we've done in the past. Sometimes we get brand new things and we try to find the closest parallel. It helps to have encyclopedic knowledge of every card in the game and if we ever have a question about a card it's easy for us to boot up a game and test the interaction out ourselves.

Changes to game rules
The designers have expressed a desire to make the rules of the game more consistent. However, the process appears to be a very gradual one, with changes made due more to necessity than as part of any more comprehensive effort to adjust the rules - at least, thus far. One way rules can change over time is through the addition of new cards which highlight inconsistencies, or otherwise require game mechanics to be altered in order to allow the desired functionality.

Prior to Naxxramas, there was not a concept of 'order of play' - it was much more difficult to predict the outcome of simultaneous deaths and simultaneous deathrattles, further complicated by a concept of 'minion tiers' which gave special priority.

Shadowboxer is an excellent example of the invention of a new card causing the game's underlying mechanics to be revised. Prior to the introduction of Shadowboxer, AoE healing effects healed targets one at a time, with any triggered effects activating after each healing occurred. For example, with a Northshire Cleric on the board, a spell like Circle of Healing would heal one minion at a time, with each followed immediately by a card being drawn, before moving on to the next minion. However, this design presented a problem for Shadowboxer's design. The current mechanic at the time of the card's invention meant that with Shadowboxer's triggered effect activated after each healing, and therefore before all healing had taken place, a Circle of Healing would potentially heal the very target the Shadowboxer had just damaged, thus undoing its effects. Likely as a result of the invention of this card, the game mechanic was altered prior to the card's addition, with the result that all single-effect healing now takes place at once, before any related triggers are activated.

The introduction of Grim Patron saw a similar adjustment, with a long-standing bug in the behaviour of Warsong Commander fixed in time for the card's release, while another several month-old bug with Warsong Commander which was not related to Grim Patron was left unfixed.

While these changes are relatively minor, they illustrate how the design of future cards might cause standardisation and change to the game's mechanics. Cards which place importance on the results of behaviours which are currently inconsistent or buggy, or vary depending on cryptic factors, may cause those mechanics to be adjusted or standardised in order to avoid contradictory results, or in order to facilitate player comprehension and prediction.