Glissa, the Traitor

Three mana for a 3/3 with first strike and deathtouch already buys a near-unkillable blocker: anything that swings into it dies, and anything it swings into dies first. That body alone would be a respectable role-player. The recursion clause is what turns it into an engine. Every opponent's creature death feeds back an artifact from your graveyard, which means the card rewards a deck built to make their creatures die on your terms: a steady stream of pings, sweepers, and sacrifice effects each becomes a card-advantage trigger. Pair it with artifacts that want to die and come back, and the loop closes on itself: an artifact that sacrifices to kill a creature, returned by the very death it caused, ready to do it again. That symmetry is the design's whole conceit, and it is built into the color pair: black supplies the removal that triggers the return, green supplies the artifact-recursion sensibility, and the Phyrexian flavor ties the metal-eating predator to the cards it claws back. The friction is that the trigger keys on opponents' creatures, not yours, so the card does nothing against a creatureless opponent and asks you to keep pressure on the board rather than hoarding it. As a commander or as a midrange centerpiece, it sits at the head of a particular kind of black-green artifact attrition deck: one that grinds the opponent's creatures into fuel and never quite runs out of things to recur.