Summon Durnehviir

Create a 6/6 black and green Dragon creature token with flying, menace, and undying (When this creature dies, if it had no +1/+1 counters on it, return it to the battlefield under its owner’s control with a +1/+1 counter on it.)

Flashback {6}{b}{g} (You may cast this card from your graveyard for its flashback cost. Then exile it.)