From Pathfinder War of Immortals, which isn't enabled.

Alter Resistance

FEAT 13

Activity reaction

Frequency once per hour

Trigger You take acid, electricity, or sonic damage.

You focus on your protean forebears to change your energy resistance. The energy resistance you gain from your Proteankin lineage changes to match the triggering damage. This change occurs after the damage is dealt and lasts until the next day, or the next time you use this ability.

Pathfinder War of ImmortalsORC