Alduin, The World Eater

Flying, Menace, Trample
Alduin's Power and Toughness are equal to the
number of creatures in exile and in graveyards.
When Alduin, The World Eater enters the battlefield, destroy all creatures without flying.
When Alduin, The World Eater attacks, you
may pay {5}. If you do, return a dragon from
a graveyard to the battlefield tapped and
attacking.