Breath of Fury

The whole engine hinges on one phrase: deals combat damage to a player. Land a hit, and the Aura jumps to a fresh creature, untaps your entire board, and hands you another combat phase. Do it again, and again, and the loop only ends when you run out of unblocked creatures to carry the Aura forward. The card converts a single connecting attacker into a chain of combats, which means the real cost is never the four mana: it is the token generator standing behind it. Pair it with anything that makes a creature available on every attack (a body that returns each turn, an army-in-a-can engine, a sacrifice payoff that refills the board) and the additional-combat clause stops being incremental value and becomes a hard kill the moment the first hit connects. The wording is also its own leash: it demands damage to a player, not a creature, so a single chump-blocker breaks the loop cold, and the sacrifice-then-attach sequence spends a creature every time the chain advances. It reads like a midrange aggro enabler and plays like a combo piece wearing aggro's clothes, the kind of Aura that does nothing in a fair attack and everything the turn an opponent leaves the ground open. Wizards has revisited the extra-combat-phase space many times since, but rarely tied it this directly to an unbounded, board-fueled loop.