Mindleecher

Mutate was built on repeatability: any effect keyed to "whenever this creature mutates" fires again each time you stack another mutate spell onto the pile, and this Nightmare's payoff is theft. Every mutation exiles the top card of each opponent's library face down and hands you a standing license to play those cards straight from exile, so the design rewards a shell that keeps mutating rather than a single evolving flyer resolved once. That is the tension. The mutate cost () actually shaves a black pip off the hard-cast, so the incentive runs in your favor: mutating is both cheaper and the only line that triggers the pillage, while a straight cast leaves you a plain 5/5 flyer that closes games and steals nothing. The raid only compounds if you commit to layering creature after creature onto the pile, each addition setting off another round of exile-and-play. The trigger hits each opponent rather than targeting them, which matters twice: the theft scales with the size of the table, and it slips past player-level hexproof or shroud entirely. It also leans on black's long-running use of resource denial as a value engine, but with a wrinkle. The stolen cards never touch your hand; they sit exiled face down, playable at your leisure, so the defensive line (stripping their draws) and the offensive one (casting them yourself) both run through exile. Where mutate usually asks whether you can build one growing threat, this one asks whether that threat can also be a recurring raid on everyone else's deck.