Acid Subtype

This subtype is usually used for Outsiders with a connection to the Quasi-Elemental Planes of Acid. Acid creatures always have swim speeds and are immune to acid damage. Acid creatures have vulnerability to water. Unless otherwise noted in the creature’s description, a water based effect or spell deals 1d4 points of damage per Spell Level to a creature with this subtype, unless otherwise noted (in either the monster’s description or the spell description). The creature usually receives a save (Fortitude or Reflex) for half damage.
 

Creatures With the Acid Subtype