Mana

Mana is the resource used in Hearthstone to play cards and use Hero Powers, each of which has a mana cost that must be paid to use it. The supply of mana is represented by Mana Crystals, displayed at the bottom right of the screen. This supply automatically increases and refills each turn, although certain cards can also affect it. Mana is the only resource used in Hearthstone, and is the primary limiting factor on the play of cards.

A player's mana is displayed in-game with two numbers:
 * The first is the number of available mana (also referred to as current mana, or simply mana).
 * The second is the number of permanent Mana Crystals (also referred to as maximum mana).

On the right of these numbers, the statuses of Mana Crystals are displayed visually with different icons: filled / empty / Overloaded / pending Overloaded.

Mana Crystals
Mana Crystals are usually permanent, although some effects explicitly grant temporary Mana Crystals for that turn only.

Permanent Mana Crystals can be in one of the following statuses:
 * filled Mana Crystals (displayed with a glowing blue icon) increase also the amount of available mana, and thus can be used to pay mana costs.
 * empty Mana Crystals (displayed with a darkened blue icon) cannot be used to pay mana costs until they are refilled.
 * Overloaded Mana Crystals (displayed with a gray padlock icon) cannot be used to pay mana costs until they are unlocked and refilled.

Effects that give Mana Crystals for "this turn only" (Innervate, The Coin, Counterfeit Coin, Gallywix's Coin) grant temporary Mana Crystals, which increase available mana for that turn but do not affect maximum mana.
 * Visually, temporary Mana Crystals are displayed to the right of permanent Mana Crystals or, if there is no room, they appear to refill existing empty Mana Crystals (as usual, granting temporary Mana Crystals to a player with 10 available mana has no effect).
 * The mana in temporary Mana Crystals is always spent before the mana in permanent Crystals. When their mana is spent, temporary Mana Crystals disappear rather than becoming empty.
 * Temporary Mana Crystals cannot be Overloaded nor pending Overloaded, and are not destroyed by abilities that destroy Mana Crystals, despite some visual bugs may occur (see below).

Maximum mana
The number of permanent Mana Crystals, called maximum mana, is displayed by the second number of the mana counter at the bottom right of the screen.

Players begin the game with 0 permanent Mana Crystals.

Permanent Mana Crystals can be gained in the following ways, up to a maximum of 10:
 * At the start of each player's turn (including the first turn of the game), that player gains a new permanent Mana Crystal (and all of their non-Overloaded Mana Crystals are refilled).
 * Some effects (Wild Growth, Mire Keeper, Darnassus Aspirant's Battlecry, Jade Blossom, Pilfered Power) explicitly give empty Mana Crystals, thus increasing maximum mana but not available mana.
 * All other effects that give Mana Crystals to a player (Nourish, Astral Communion, Grove Tender, Arcane Golem, Demonfuse) grant filled Mana Crystals, thus increasing both available and maximum mana accordingly.
 * A player can never have more than 10 maximum mana.

Effects that destroy Mana Crystals (Felguard, Blastcrystal Potion, Darnassus Aspirant's Deathrattle) permanently destroy permanent Mana Crystals, starting from empty ones, decreasing maximum mana up to a minimum of 0.
 * If a player is forced to lose a filled Mana Crystal (because all of their permanent Mana Crystals are filled) their available mana will be reduced accordingly for the current turn too. Otherwise, their available mana is not reduced for the current turn, but only for subsequent ones.
 * A player can never have less than 0 maximum mana.
 * Example: If a player repeatedly plays Felguard to destroy all of their Mana Crystals and then plays another Felguard, nothing happens.
 * Example: A player that has one of their Mana Crystals destroyed will have one less mana each turn until they reach 10 Mana Crystals. Thus, if that player was already at 10 Mana Crystals, they will lose a Mana Crystal but simply regain it at the beginning of their next turn.

Available mana
The number of currently filled Mana Crystals, called available mana or current mana, is displayed by the first number of the mana counter at the bottom right of the screen and represents the amount of mana that is still available for the player to use cards and Hero Powers that turn.

Available mana can be increased in the following ways, up to a maximum of 10:
 * At the start of each player's turn all of their non-Overloaded Mana Crystals are refilled, increasing available mana accordingly. (This means that mana left unspent by the end of the turn is essentially wasted, since it is refilled anyway at the beginning of the next turn.)
 * Effects that give Mana Crystals for "this turn only" (Innervate, The Coin, Counterfeit Coin, Gallywix's Coin) grant temporary Mana Crystals, which increase available mana for that turn.
 * Effects that give permanent filled Mana Crystals to a player (Nourish, Astral Communion, Grove Tender, Arcane Golem, Demonfuse) increase both available and maximum mana accordingly.
 * Kun the Forgotten King's second effect refills all of his controller's non-Overloaded Mana Crystals, increasing available mana accordingly.
 * Lava Shock and Eternal Sentinel unlock and refill all currently Overloaded Mana Crystals, increasing available mana accordingly, and remove all currently pending Overloaded mana.
 * A player can never have more than 10 available mana (thus, for example, playing Innervate with 10 available mana will have no effect), but effects that grant extra Mana Crystals or that refill the player's Mana Crystals can be played after some mana is expended, thus allowing a total expenditure of more than 10 mana in that turn. Effects that grant one or more permanent Mana Crystals while the player already has 10 permanent Mana Crystals generate an Excess Mana for the player instead.

Available mana can be reduced in the following ways:
 * When a player spends mana to play cards or use Hero Powers, their available mana is reduced accordingly. This is the most frequent way a players' available mana is reduced, up to the beginning of their next turn when their Mana Crystals are refilled and they can spend their mana again.
 * Each card and Hero Power has a specific mana cost, displayed as a number inside a blue crystal in the upper left corner of each card and at the top of each Hero Power, which represents the amount of mana that must be expended in order to play that card or use that Hero Power. Some effects can decrease or increase these mana costs: for a list of such effects and how they interact with each other, see Mana cost.
 * Cards can be played and Hero Powers can be used only if their mana cost can be paid. Note that the mana cost must be paid before any card effects are taken into account, so cards like Lava Shock or Nourish cannot be cast if the player has less than the stated mana cost, even if the card itself would free up enough mana.
 * Mana spent is taken from temporary Mana Crystals first (which disappear after being used), and any exceeding cost is then taken from permanent Mana Crystals (which become empty).
 * Effects that destroy Mana Crystals (Felguard, Blastcrystal Potion, Darnassus Aspirant) reduce available mana only if they are forced to destroy filled Mana Crystals.
 * The spend mana ability consumes all the player's available mana as part of the card's effect, producing an effect proportional to the amount spent. Cards that spend mana can be played even when there is no mana left to consume (although in that case the ability will simply have no additional effect).
 * Cards with Overload that are played from the hand reduce the amount of mana available the next turn by the stated amount. More precisely, playing a card with Overload causes the stated amount of Mana Crystals to become pending Overloaded (a padlock icon appears beneath a permanent Mana Crystal for each point Overload), and at the start of the next turn that Mana Crystals will become Overloaded: the padlocks will move up and block out the player's Mana Crystals, effectively preventing them from being refilled and used for that turn.
 * A player's current and/or pending Overloaded Mana Crystals has no upper limit. For example, a player can Overload more mana than they will have the next turn: even if the user interface will only display Overload equal to the player's maximum mana, the excess will still be registered and will affect mana-generating effects like The Coin. . Once the Overload has been matched, any further mana generated will be usable by the player, and will be reflected in the mana counter.
 * Overload affects available mana for the next turn only, even if it is greater than that turn's maximum mana: current Overload will disappear (regardless of its amount) at the beginning of the player's next turn, when it is substituted by previous turn's pending Overload.
 * Example: If a player plays two Dust Devils on turn two, on the next turn they will have 4 Overloaded mana despite having only 3 Mana Crystals: this mana deficit will not carry over to subsequent turns, thereby allowing the player to avoid paying that part of the Overload cost at all.
 * Overloaded and pending Overloaded mana are not displayed for the opponent: players trying to estimate the opponent's available mana next turn can use the history to check the cards played that turn.


 * Available mana has no lower limit and thus, with enough Overload, "actual" available mana can be negative: although the game interface simply displays negative available mana as 0 and gives no sign at all that excess Overload remains, the excess will still be registered, and will counter mana generation through effects like Innervate.
 * However, no amount of Overload will prevent the player from playing 0-Cost cards: since these cards cost no mana, the player's current mana total is irrelevant.

Visual bugs

 * If a player playing Nourish, Grove Tender or Astral Communion has not enough room for the new Mana Crystals, they will replace any empty Mana Crystals (usually some of those emptied in order to play that card) or, if there are not, any Overloaded Mana Crystals (despite Overloaded Mana Crystals visually appear to remain locked, the available mana counter is increased correctly). However, pending Overload is not affected, and will be reduce available mana for the next turn as usual.
 * Effects that destroy Mana Crystals (such as Felguard) sometimes seem to destroy a pending Overloaded Mana Crystal: however, despite the visual appearance, losing (or gaining) maximum mana has no effect on your pending/current Overload.
 * While The Coin works correctly in relation to excess Overloaded mana, the visual effect does not: playing The Coin while having more Overloaded mana than current Mana Crystals will create a new, fully charged, non-padlocked Mana Crystal; however, the player will not be able to draw mana from that Mana Crystal, due to Overload.
 * If you have 0/10 mana due to 10 Overloaded Mana Crystals and play The Coin, the mana counter will correctly display 1/10 mana, but visually you will still have 10 locked Mana Crystals and no filled one. Similarly, if you have 10 permanent Mana Crystals, some of which are Overloaded and the remaining ones are filled, and gain some temporary Mana Crystals, their mana will be usable and displayed in the mana counter although displayed Mana Crystals are still Overloaded/filled as before.

Strategy
The limited but slowly-increasing supply of mana serves to delay and add pace to the game, preventing players from simply playing their most powerful cards on round one. It also crafts the game into distinct phases, with higher-value cards only becoming playable in later rounds. The increase of available mana over the course of a match is referred to as the mana curve, and is a key strategic concept, both during play and in deck building.

As one of the key limiting resources in the game, effective mana management is essential for achieving victory in Hearthstone. While generally it is ideal to make use of all available mana each turn to maintain tempo, in practice it is sometimes wiser to hold back cards until the right time, especially if planning a combo. While this may lead to mana being 'wasted', taking a more cautious approach to card playing can win games. Hero Powers, while intentionally mana-inefficient, may be helpful for making use of mana every turn without consuming cards.

The mana cost of a card determines which round it will become available to play, as well as which cards it can be used in combination with. This concept is used in deck building to ensure viable options each turn, and can also be used to predict which cards may be played on certain rounds, such as Mind Control generally only becoming playable from round 10 onwards.

Related cards
The following cards have effects that specifically alter a player's available and/or maximum mana (these effects are most commonly found in druid cards). Not listed here are cards with Overload (found only in shaman cards), which reduce available mana for the next turn (see Overload for a list).

For a list of cards that modify mana costs rather than available/maximum mana, see Mana cost instead.

Trivia

 * Unlike in many other games, including World of Warcraft, in Hearthstone mana is apparently not an arcane or purely magical power, and can be wielded by heroes of all classes. Notably, warriors, rogues and hunters normally use resources other than mana.