Karn, Living Legacy

Powerstones are the design idea that makes this Karn coherent, and they resolve a problem that has dogged colorless ramp for years: acceleration you cannot funnel into a cheating-out-a-bomb combo turn, because Powerstone mana refuses to pay for nonartifact spells. That constraint is what lets a four-loyalty planeswalker generate a token every turn without spiraling out of control; the ramp is real but fenced into the artifact half of the board. The minus one is a mana-sink card-selection ability, a smoothing valve that turns those Powerstones (and any other flood of colorless) back into cards. And the ultimate closes the loop: an emblem that converts every untapped artifact you control into a repeatable ping. The three abilities are a single loop wearing three faces: make artifacts, dig for the payoff, then burn the opponent out by tapping the artifacts you made. Where earlier Karn incarnations reached for the game's biggest artifact payoffs or exiled the top of a library, this one is deliberately self-contained, a colorless engine that funds itself. What it wants is a critical mass of artifacts to feed the emblem and mana-hungry activated abilities to spend Powerstone mana on, whether those artifacts are creatures or not. That is a narrower, more honest brief than the character's history of format-warping designs would suggest, and the tightness is the point.