Witherscale Wurm

A 9/9 with its survival logic wired backward, and the trick is reading which way the counters flow. The first ability hands wither to whatever fights it, which sounds like a weapon until you trace the result: that blocker or attacker now whittles the Wurm down with -1/-1 counters instead of ordinary combat damage, and counters do not wear off when the turn ends. A single block can leave a permanent dent in the body. The cleanup comes only from connecting with a player: do that, and every counter sloughs away, restoring the full 9/9. So this is not durable in any one fight; it is durable across cycles, accumulating shrinkage when it gets walled and washing clean the instant it lands a hit. The timing is the catch. That reset fires on damage to an opponent specifically, not to a creature or planeswalker, so an attacker held off by chump blockers stays small and never gets its restore. And nothing in the design answers removal, sacrifice, or edicts; the engine only spins when creatures are actually allowed to meet in combat. It reads as green's commentary on the -1/-1-counter texture of its era: a finisher that turns the grind mechanic back on itself, then quietly bets you can push damage through before the arithmetic catches up with the body.