Cubwarden

Mutate's central bargain is verticality: you stack a pile into one enormous body and lean on a single triggered ability to compound its value with each new spell you commit. This shares that "whenever this creature mutates" trigger with the rest of the mechanic, but where most payoffs pump the pile itself or reach for the graveyard, this one spits out board width. Two lifelink Cats every time the pile grows means the reward scales sideways: keep feeding the stack and you keep manufacturing bodies, so a removal spell answers the tower without answering the tokens it already left behind. White's go-wide instinct and its lifegain instinct usually live in separate cards; here they ride the same trigger, and the defensive 3/5 frame is a deliberate choice, because the tokens are meant to carry the offense while the base body just holds the ground. Lifelink across the whole team bends any race in your favor the longer the pile survives, and each mutation reloads the board rather than just growing the number on top. It is a payoff piece rather than an engine, built so the fifth mutation still matters as much as the first: not by hitting harder, but by hitting from three angles instead of one.