Memnarch

Two abilities that bend the rules of object identity rather than the rules of combat: one turns any permanent into an artifact, the other steals any artifact outright. Stack them and the loop is obvious. Make an opponent's creature an artifact, take it. Make their land an artifact, take it. Given enough mana, the Soul of Mirrodin annexes the entire board one permanent at a time, which is exactly the flavor a self-appointed god of an artifact plane should carry. Neither ability decides anything in isolation: the first only rewrites a type line, the second only reaches things that already say artifact. The win lives in the interaction between them, repeated, and the cost of repeating it is the only brake. Seven mana to deploy the body, then activations that pile up faster than most decks produce mana, which is why Memnarch reads as an engine you assemble around rather than a finisher you cast. Blue's artifact-matters lineage runs long, but most of it cared about your own artifacts; here the design weaponizes artifact-typeness as an offensive vector, rewriting what the opponent controls into something it can claim. The 4/5 body is almost incidental: a Wizard expensive enough that nobody plays it to attack, only to start grinding the table into its own.