Abyssal Harvester

The activation window is the whole design here: it only steals from creatures that hit a graveyard this turn, so the tap ability is a reactive tool bolted to combat and removal rather than a slow reanimation engine that grazes on old corpses. That constraint turns it into a tempo-and-value drain: every kill spell you cast, every creature that dies blocking, every sacrificed creature becomes a candidate the moment it happens, and the Harvester answers by handing you a fresh copy. The self-cannibalizing clause is where the tension lives. Because it wipes your other Nightmare tokens each time it fires, the copies are explicitly non-cumulative: you never assemble a board of stolen bodies, you rent exactly one at a time, and each activation trades the last thing you took for the next. That reframes the card from a swarm-builder into a serial upgrade machine, always angling to trade up as bigger creatures die around it. The token retains everything the original had (its abilities, its enters-the-battlefield triggers, its own type line plus Nightmare), so the ceiling scales with whatever your opponents are unfortunate enough to lose in a given turn. A modest 3/2 that asks you to build a board state where death is constant and immediate, then converts that churn into a single, ever-improving stolen threat.