Shifty Doppelganger / Unsteter Doppelgänger
3U, Remove Shifty Doppelganger from the game: Put a creature card from your hand into play. That creature gains haste until end of turn. At end of turn, sacrifice that creature. If you do, return Shifty Doppelganger to play.
http://From Odyssey Frequently Asked..., May 17, 2003:
-) If you have any creature cards in your hand when Shifty Doppelganger's ability resolves, you must put one of them into play.
-) If the creature you put into play is still in play under your control at the end of the turn, you must sacrifice that creature.