Loki

You may have Loki enter the battlefield as a
copy of any creature on the battlefield or in a
graveyard, except its name is Loki.
At the beginning of your end step, if Loki is in
your graveyard, you may return it to the
battlefield tapped during your next upkeep step.
Well, he's been dead before. But this time... I
think it really might be true.
-Thor