Soulshift is a keyword ability.
Amber controls a and has a and a in her graveyard. When Gibbering Kami its soulshift 3 will trigger, this means that he can bring back the Wandering Ones, as it has a CMC of 1, but not the Kami of Old Stone, as it has a CMC of 4, which is higher than the max of three. It also can't bring itself back.
- 702.45a. Soulshift is a triggered ability. "Soulshift N" means "When this permanent is put into a graveyard from the battlefield, you may return target Spirit card with converted mana cost N or less from your graveyard to your hand."
- 702.45b. If a permanent has multiple instances of soulshift, each triggers separately.