Kosviel, Angel of Chaos

Flying
Ward—Sacrifice a permanent
Whenever you cast your first spell during each of
your turns, exile the top card of your library. If
it's a nonland card with mana value 4 or less,
you may cast it without paying its mana cost. If
you don't cast the exiled card, put it into your graveyard, then Kosviel, Angel of Chaos deals 3
damage to any target.