Antedeum, the First

Antedeum, the First's toughness is equal to
the number of cards in your library.
When you attack with Antedeum, the First,
exile the top card of any player's library. You
may play that card without paying it's mana cost
as long as it's in exile.
If Antedeum is exiled or put into the graveyard,
instead return it to the battlefield.