Genestealer Patriarch

Infection is usually a poison clock aimed at the opponent's life total, but here the counter is repurposed into a conversion engine, and that reframing is the whole design. The attack trigger seeds counters onto creatures the defender controls, and the second ability harvests them: any counter-bearing creature that dies returns to you as a Tyranid copy. The result is a slow-motion theft mechanic. You are not killing your opponent's board so much as annexing it, one death trigger at a time, and each stolen creature enters as a copy with the Tyranid type stapled on top of whatever it already was, which happens to matter in a deck that cares about Tyranid density. The catch is that neither half closes the loop alone: the attack trigger only tags a target, and the copy trigger only fires when something already marked dies, so the Patriarch wants ways to force those marked creatures into the graveyard. Since the counters land on the defending player's side, the enabling has to reach across the table: targeted removal that can hit the marked creature, edict effects that make the opponent sacrifice, or forced combat that trades the tagged creature away. That dependency on outside interaction is what keeps a five-mana body from running away with a game on its own. It reads as flavor-forward (the genestealer cult infiltrating and subverting a host population, rendered as a mechanic), but the underlying structure is a genuinely unusual take on counter-matters: a counter that neither buffs nor poisons but converts, harvesting a return that grows with every marked creature you can persuade to die while wearing your mark.