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

Terrain Form

FEAT 10
Activity 1 action
Archetype Mummy
Prerequisites Mummy Dedication

Frequency once per day

You crumble to pieces, becoming composed of the very terrain to which you're bound, with the effects of the gaseous form spell, or you reconstitute into your normal form. The substance you're formed of depends upon your bound terrain, and the action gains the corresponding trait or traits.

Arctic Snow (water)

Desert Sand (earth)

Mountain Cloud (water)

Swamp Mud (earth, water)

Pathfinder Book of the DeadOGL