Loki, God of Lies

Threaten effects have always been a study in tempo: pay for the theft, swing, hand the creature back at cleanup, a one-shot burst that lives and dies on the attack step. This villain rewires that transaction into a rider on the spells you were already casting. Any spell that targets exactly one creature (a combat trick aimed at an enemy blocker, a copy effect, an aura, a protective pump pointed the wrong way) folds a control-magic clause into mana committed elsewhere. The trigger cares only about how many creatures the spell targets, not what it does, so it wants spells that leave the stolen body alive and useful rather than a removal spell that kills the thing out from under you. The interesting restriction is timing. The control effect lapses at cleanup, and the untap-and-haste bonus fires only on your own turn, which locks the theft into a single window: cast on your turn, take the blocker, untap it, swing before it reverts. A steal that fires during an opponent's turn buys you a defensive body for that turn and nothing more, since you give the creature back before you ever untap for combat. The two clauses only pay off in one direction, and that asymmetry is what the design is built around; the beater it rides in on is incidental. The real return sits in how many of your single-target spells quietly grow a second mode the moment this resolves.