Prayers to the Grimroot

As an additional cost to cast this spell, exile any number of target creatures from your graveyard.
Create a legendary X/X green and black Avatar creature token that has all activated, triggered, and keyword abilities of creatures exiled to cast this spell and, "This creature's power and toughness are each equal to the number of your exiled creatures."
"We offer thee the souls of those who were unworthy to stand b