Boneyard Lurker

Mutate trades card economy for a scaling threat: you feed creatures into a pile and keep the best statline on top, but every card that goes under is a card spent to build one body. This one answers that cost directly. Its mutate trigger is a Regrowth stapled to a growing 4/4, and because it fires whenever the creature mutates, not just the first time, each subsequent piece you stack onto the pile buys back another permanent from the graveyard. That widens the return well past creatures: any permanent card in the yard, an enchantment, a dead artifact, a milled land, comes back to hand. And it patches mutate's structural weakness. A mutate stack is a house of cards; one removal spell can eat the whole investment. Recurring a permanent on the way up softens that math, so the pile has already generated value even when it dies. The two-headed casting cost, castable as a plain 4/4 or for its hybrid mutate cost, keeps it honest for decks that want the beater without the graveyard engine. Among the Nightmare Beast mutators, this is the one built to grind rather than to close, the piece that makes a long game with mutate feel less like a gamble on the top card and more like a resource loop.