Theoretical Duplication

Whenever a nontoken creature enters the battlefield under an opponent's control this turn, create a token that's a copy of that creature.

Wrong Turn

Target opponent gains control of target creature. (If an attacking or blocking creature changes controllers, it's removed from combat.)

Visions of Duplicity

Exchange control of two target creatures you don't control.
Flashback {8}{U}{U}. This spell costs {X} less to cast this way, where X is the greatest mana value of a commander you own on the battlefield or in the command zone. (You may cast this card from your graveyard for its flashback cost. Then exile it.)