Protean Hydra

Most damage-prevention shields read as defensive insurance; here the prevention clause is the engine. When something would deal damage, that damage is prevented and the equivalent number of counters comes off instead, and each removed counter pays back double at the next end step. The result is a creature that grows when you try to kill it with damage: a two-counter hit erased now becomes four counters added later, so even a small ping feeds the loop rather than picking at it. The only damage that profits is a coordinated, same-turn volley large enough to strip every counter before the end-step trigger can refill them: anything short of that hands you a bigger Hydra. The honest counter is removal that does not deal damage at all: exile, destruction, sacrifice, minus-toughness, and bounce all sidestep the prevention clause entirely, because nothing about death triggers, edicts, or -X/-X interacts with the damage-prevention shield. That split is what the whole card is organized around: against the half of removal that works by dealing damage, this is one of the hardest green creatures to fight through profitably; against the half that does not, it is no more resilient than its X would suggest, since the engine never triggers. The replacement-into-end-step timing also opens a window, since the counters return at the beginning of the next end step rather than immediately, leaving the creature briefly diminished after combat. A Hydra built to punish the burn-and-fight school of removal specifically, and to fold cleanly to everything else.