Firstborn of Seguul

Cast Firstborn of Seguul only from your graveyard. When Firstborn of Seguul enters the battlefield, if it was not cast, you loose the game.
Deathtouch, Trample, Haste
When Firstborn of Seguul enters the battlefield, each player sacrifices all other creatures. Create a 2/2 black zombie creature token with haste for each creature sacrificed this way.