Priest of Forgotten Gods does not have summoning sickness.
You control at least one additional creature.
Steps
Activate
Priest of Forgotten Gods by tapping it, sacrificing
Reassembling Skeleton and any other creature.
When
Reassembling Skeleton and the other creature die,
Priest of Forgotten Gods triggers twice, untapping
Priest of Forgotten Gods.
Resolve the
Priest of Forgotten Gods ability from step 1, causing any number of players to lose 2 life and sacrifice a creature, and you to add ({B} magic symbol) ({B} magic symbol) and draw a card.
Activate
Reassembling Skeleton by paying ({1} magic symbol) ({B} magic symbol) , returning it from your graveyard to the battlefield.
Tormod triggers, creating a 2/2 Zombie creature token.