Spellbook Duel


 * "Choose your spellbook carefully, champion! Pick 10 cards, and anytime you would draw a card, you instead Discover a copy of a card from your deck."

 is a Tavern Brawl. It debuted on January 18, 2017.

Overview
This Tavern Brawl sees players doing battle with custom decks composed of 10 cards chosen by the player, with only 1 copy of each card allowed. At the start of the game, both players mulligan as normal, but at the start of each turn instead of drawing a card, the player will instead Discover a card from three options matching cards currently in their deck. This Discover does not remove the card from the player's deck, but instead places a copy into their hand.

Card draw effects do not operate normally during this Brawl: instead of drawing a card from the deck, the player has a copy of Peruse added to their hand. (This is technically considered card draw but does not come from the deck.) This 1 mana spell can then be used to Discover a card in the same way that players gain new cards at the start of each turn. Put into hand effects similarly generate copies of Peruse.

The combination of these special rules means the player is unable to draw cards normally, but the contents of the deck can still be altered through put into battlefield, shuffle into deck, and replace effects, as well as unique cards like Fel Reaver and Tracking. Because the deck acts as a source for each turn's Discover effect, altering the contents of the player's deck will affect which options the player is able to Discover.

Known bugs

 * Playing Gnomish Experimenter will sometimes cause a a glitch resulting in a strange interaction between the Discover mechanic and the Experimenter's Battlecry, replacing a minion before the Discover screen pops up, and the Chicken card will be offered instead of the original minion that it replaced.

Strategy

 * Deathlord is an extremely valuable card, as not only do you get a 2/8 with Taunt, but you can also permanently remove a card from your opponent's Discover pool. With luck you can remove some of the opponent's most valuable cards early on, all but removing them from the match.
 * Gnomeferatu has a similar effect to Deathlord in the form of a Battlecry instead, and also removes other cards in addition to minions. Dropping multiple copies of this minion, alongside Deathlord and Brann Bronzebeard, can strip away most of your opponent's resources unless deck-filling cards such as Jade Idol, Gang Up and Forgotten Torch are used.
 * One method of winning is to make a Jade Golem deck. Using the Druid's Jade Idol, one can summon as many as 3 or more golems a turn and quickly obtain golems with 7/7 or more early in the game.
 * A powerful strategy is to play mage and fill your deck with Sorcerer's Apprentice, Flamewaker, Gadgetzan Auctioneer and some cheap spells. As long as you have at least one Sorcerer's Apprentice, your cards will cost 0 mana and you can indefinitely play cards thanks to Gadgetzan Auctioneer. At the same time, your Flamewaker will deal heavy damage to your opponent, and will activate from every Peruse played.
 * Similarly, Gadgetzan Auctioneer and Innervate can provide a near-infinite draw engine. Combine this with Kun the Forgotten King and Fandral Staghelm for large amounts of armor in a single turn.
 * Reno Jackson is also an extremely valuable card, since it always will activate (shuffle into deck effects aside) and you can have more than one copy of him in hand. Other "no duplicates" cards are similarly reliable: Inkmaster Solia, Kazakus, Raza the Chained and Krul the Unshackled.
 * Open the Waygate is extremely easy to complete in this Tavern Brawl because all the spells from your deck that you discover and Peruse count toward quest progression.
 * Radiant Elemental has great synergy in this Brawl, as a single Elemental on the board provides you with free copies of Peruse, Power Word: Shield, Inner Fire and so on, potentially allowing for a one-turn KO.
 * Skulking Geist can be a good tech in this Brawl as it instantly removes all copies of Peruse in your opponent's hand, and counters the aforementioned Jade Idol and Radiant Elemental strategies, albeit only in the mid to late game due to its Mana cost.