pf2e.fyi
From Pathfinder Season of Ghosts Hardcover Compilation, which isn't enabled.

Undying Flesh

ACTION

You're a fearsome and vengeful spirit, and certain physical weapons seem to have little effect on you. Choose bludgeoning, piercing, or slashing; you gain resistance 10 to that damage type. Whether your resistance to that damage manifests in the form of a weapon appearing to pass harmlessly through your body or by appearing to leave grievous wounds that you ignore is left to you to decide, but once the decision is made, you can't change it.

Pathfinder Season of Ghosts Hardcover CompilationORC