Goatnap

Threaten with a punchline. The template it draws from is old and durable: pay a bit of red, borrow a creature for the turn, untap it, give it haste, and swing with the opponent's own best threat before handing it back at cleanup. The clever part is the reward clause that never triggers unless you build for it. Steal any creature and you get the standard effect; steal a Goat and you get an extra +3/+0, a rider that costs nothing to include and does nothing in almost every game you draw it. That gap between the baseline utility and the tribal bonus is the whole joke: the card is functional in any red deck as a tempo-and-reach play (a sacrifice-outlet feeder, a race-closer, an untap-and-attack trick), while the Goat clause exists purely as a wink at players who would go out of their way to assemble a stable of Goats worth pumping. It is design that treats a creature type nobody was building around as the setup for a gag, then makes the gag mechanically real rather than flavor text. The result is a serviceable temporary-theft spell wearing a bit, and the bit is the reason anyone remembers it.