True Polymorph

Polymorph's older cousins asked you to gamble: Polymorph itself pulls a random creature off the top, Proteus Staff shuffles until you hit one. This one does the same trick with the gamble removed and the targets doubled. You pick the thing you want to transform and the thing you want it to become, and the copy is total: the target becomes the second permanent, name, types, abilities, and all. The instant speed is the load-bearing detail. Cast at the wrong time, a copy effect is a party trick; cast in response to something on the stack, it rewrites the board mid-combat, mid-block. You can turn your opponent's bomb into a bear while its trigger is still waiting to fire, or hand yourself a second copy of the best thing in play. And the effect sticks: it carries no duration clause, so unlike the layered end-of-turn copy tricks that expire on their own, this rewrite stays in place unless a later effect overrides it. Because it reaches artifacts as freely as creatures, the puzzle box is bigger than a single removal spell suggests: any artifact can become any creature, any creature any artifact, assembled in whatever order the stack allows. Six mana at instant speed is a steep price for a shape-change, but what that price buys is closer to unlimited than the type line lets on.