Identity Thief

Most copy effects take a snapshot the moment they resolve: clone the creature, keep the new body, and the original stands untouched. This one inverts the deal. When the attack trigger resolves, the targeted creature is exiled, this Shapeshifter assumes its form until end of turn, and the exiled card returns under its owner's control at the next end step. The copy is the loan; the removal is the rent. That return clause works in two directions at once. Pointed at an opponent, it is a temporary removal spell bolted to a threat: their best blocker leaves for the swing, and the borrowed body crashes in with whatever combat-relevant text it brought. Pointed at your own board, the end-of-turn return is a flicker that re-triggers an enters-the-battlefield ability while you wear the creature's stats for a turn. The 0/3 base body is what pays for all this: on a turn with no legal target to become, it attacks for nothing, so the card is only ever as good as the best creature it can point at. Because the steal is built on the stack and a chosen target, the engine is also exposed there. Remove the target in response to the attack trigger and the ability has no legal object to resolve against; it fizzles, and what charges in is the bare 0/3 Shapeshifter, attack trigger spent and nothing borrowed. The same targeting that lets it borrow the strongest creature on the table is the seam an opponent gets to attack.