The weekly Tavern Brawls in Hearthstone: Heroes of Warcraft can be pretty silly sometimes, enabling plenty of weird, hyperspecific situations you would never encounter in a normal round. This week's installment, the Battle of Tol Barad, gives players a free 0-cost spell equal to the mana cost of any minions they play, allows players to achieve an otherwise-impossible combo that kills everything on the board — including both competitors.
Here's how it works: because there's only one 9-cost spell in all of Hearthstone, playing any 9-drop in this Tavern Brawl guarantees players of that spell a free 0-cost copy of Tree of Life, a Druid spell that 'restores all characters to full health,' including both minions and player heroes. Priest players are probably familiar with Auchenai Soulpriest, a minion that makes it so all healing effects actually deal damage instead. Thanks to this Tavern Brawl, these Druid and Priest cards can coexist in the same deck, creating a combo in which everyone dies — not only every minion on the board, but both players, resulting in a simultaneous defeat on both sides of the board.
This combo is an excellent example of what makes Tavern Brawls frequently so great: by supplying a bizarre ruleset for players to experiment with every week, Blizzard opens the game up to all sorts of new and strange possibilities — even silly and kind of useless ones like this.