pf2e.fyi
From Pathfinder Book of the Dead, which isn't enabled.

Spirit's Mercy

REACTION
Activity reaction

Trigger You take vitality or void damage, or you take any type of damage caused by a haunt, ghost, or other incorporeal undead
Cost 1 spirit wisp or remnant

Effect You purify a spirit by having it perform a final act of mercy to lessen the damage caused by another spirit. This grants you resistance to vitality and void damage (or resistance to all damage if caused by a haunt or incorporeal undead) against the triggering effect. If you expend a spirit wisp, the resistance is equal to twice your level. If you expend a spirit remnant, the resistance is equal to three times the level of the incorporeal undead or haunt from which you gained the remnant.
Pathfinder Book of the DeadOGL