Chthonic creatures are native denizens of the Elemental Planes of Earth. They produce acid, which they use to help them burrow quickly through the dense rock of their homes. This template can be applied only to a nonoutsider that has none of the following subtypes: air, cold, earth, fire, or water. A chthonic creature’s CR increases by 1 only if the base creature has 5 or more HD.
Rebuild Rules: Type The creature gains the earth subtype; Senses gains darkvision 60 ft.; Defensive Abilities gains DR and resistance to acid as noted on the table below; Speed gains a burrow speed equal to half its highest speed (its tunnels always collapse behind it, and never leave behind a usable passage); Attacks gains bonus acid damage as noted on the table below on attacks with natural weapons.
Pathfinder Player Companion: Monster Summoner’s Handbook © 2015, Paizo Inc.; Authors: Alexander Augunas, Tyler Beck, Anthony Li, Luis Loza, David N. Ross, Owen K.C. Stephens, and Linda Zayas-Palmer.