Green Dragon

The enters trigger reads like a battlefield-wide arming device: for the rest of the turn, any damage an opponent's creature takes becomes lethal, no matter how much toughness it has left. That reframes the whole rest of your turn. A one-damage ping, a burn spell that would ordinarily just soften a blocker, an attack that trades down on paper: each becomes a kill switch while the trigger is live. The window is deliberately narrow, expiring when the turn ends, so the payoff has to be spent immediately rather than held as a standing lock. Resolve the Dragon, then convert whatever incremental damage you can muster into a board sweep before you run out of turn. The 4/4 flying body is almost incidental to that plan; it can attack the following turn like any beater, but by then Poison Breath has lapsed. The tactically interesting wrinkle is that nothing forces the sweep to happen on your own main phase: any way to make it enter with the trigger live (a flash enabler, a blink effect, an instant-speed reanimation) turns a combat-arming device into a defensive one, arming a block or a burn response mid-turn. What the design borrows from is the fight-and-deathtouch school of green removal, where the color's answer to problem creatures has always been to trade combat math for a kill. Here that logic is decoupled from a single fight and broadcast across every damage source in one turn, with the cost being that green makes you build the damage yourself and cash it in before the window closes.