Thornbite Staff attached to Priest of Forgotten Gods.
Priest of Forgotten Gods does not have summoning sickness.
You control at least one Zombie, and at least one additional creature except Gravecrawler or the Zombie.
Steps
Activate Priest of Forgotten Gods by tapping it and sacrificing Gravecrawler and any other creature.
When the creatures die, Priest of Forgotten Gods triggers twice, untapping itself.
Resolve the Priest of Forgotten Gods ability, causing any number of opponents to sacrifice a creature and lose 2 life, and causing you to add ({B} magic symbol) ({B} magic symbol) and draw a card.
Cast Gravecrawler from your graveyard by paying ({B} magic symbol) .
Insidious Roots triggers, creating a 0/1 Plant creature token.