Witch of the Moors
The engine here runs on the cheapest trigger in black's toolkit: any lifegain at all, anywhere in the turn, and the end step becomes an Edict plus a graveyard buyback. That "if you gained life this turn" condition is doing the heavy lifting, because black has never been short on incidental lifegain (a single drain, a Zulaport Cutthroat ping, a Sword of Light and Shadow connection, a Gray Merchant of Asphodel resolving). Meet it, and each opponent hands over a creature while you pull a creature card back from your own graveyard to your hand, which means the loop can refuel the very sacrifice fodder that keeps the lifegain flowing. The deathtouch body is not incidental either: it makes attacking into her a losing proposition and gives her enough defensive spine to survive to the end step she cares about. The two effects point in opposite directions, and that is the whole appeal. Most attrition pieces either strip the opponent's board or rebuild your hand; this does both in one trigger, and the returned card is a target you choose, not a top-of-library gamble. The condition is the tax, and it is one a black deck pays without contorting to do so. Left unanswered for even one cycle of turns, she converts a passive lifegain shell into a recurring two-for-one that grinds a symmetrical board into a very asymmetrical one.
