Oracle Text

Legendary Creature — Unicorn

{3}: Exile another target creature you control, then return it to the battlefield under its owner's control. Whenever another creature you control enters, you may pay {G/W}. If you do, put a +1/+1 counter on it. If it's a Unicorn, put two +1/+1 counters on it instead. ({G/W} can be paid with either {G} or {W}.)