Geist Soulbinder

Coalesce (When you cast this spell, you may sacrifice
any number of spirit you control. This spell cost
{1} less to cast for each spirit sacrificed this way.)
At the beginning of your upkeep, Create a 1/1
black Spirit creature token.
"Following the geist procession, we arrived at a valley
where hundreds of geists were converging. At the
center, we could see a single geist seemingly gathering
and binding all the others."