Azathoth

You can't cast this spell unless you own a card
named "Azathoth's Lullaby" in exile and there
are no creatures named "Servitor" on the battlefield.
When Azathoth enters the battlefield, exile all permanents and all cards from each player's hand
and graveyard.
Azathoth's power and toughness are equal to the number of cards that you own outside the game.