This creature looks like a crystalline caterpillar.
Caterprism CR 6
Speed 30 ft., burrow 20 ft.
Melee bite +11 touch (1d6+5) or 4 claws +10 (1d6+5)
Space 10 ft.; Reach 5 ft.
Special Attacks crystal breath, crystalline mandibles
Str 20, Dex 12, Con 18, Int 4, Wis 13, Cha 11
Base Atk +6; CMB +12; CMD 23 (can’t be tripped)
Feats Iron Will, Power Attack, Weapon Focus (bite)
Skills Climb +12, Perception +8, Stealth +6, Survival +8
Three times per day, as a standard action, a caterprism can spew forth a crystalline silk-like substance in a cone to a range of 20 feet. The substance instantly solidifies to a rock-like hardness, forming needlesharp spears of crystal that impale those in the area and deal 3d6 points of piercing damage. A DC 17 Reflex save halves the damage. The save DC is Constitution-based.
The mandibles of a caterprism are so sharp that they can bite through nearly anything. The bite attack of a caterprism is treated like a touch attack; i.e., it ignores any armor bonus. Further, the bite of a caterprism is considered to have the vorpal special quality, and on a successful critical hit with its bite attack, the caterprism severs the head of its opponent.
Environment Elemental Planes of Earth
Organization solitary, pair, or nest (2–5)
A caterprism is from the Elemental Planes of Earth. It resembles a caterpillar made of crystal with hexagonal body segments and twelve sharply angled legs. Each body segment is about 2 feet long and contains a single pair of legs. The head of a caterprism is caterpillar-like, with large faceted eyes and huge mandibles.
Although caterprisms prefer to consume the rich minerals of their home plane, they sometimes wander through natural portals into the Material Plane. There, they create long, winding tunnels as they eat their way through the solid rock. Dwarves have been known to bring caterprisms under some degree of control, using them to help carve out new mines and dwelling places.
If it feels threatened, a caterprism’s first action is to shoot at its opponents with its crystalline silk-like secretions. It then closes to bite, or rears up and stabs at opponents with the first four of its razor sharp legs. A caterprism can eat through 1 foot of solid stone per minute, leaving behind a permanent tunnel 5 feet in diameter.
Caterprism from the Tome of Horrors Complete, Copyright 2011, Necromancer Games, Inc., published and distributed by Frog God Games; Author Erica Balsley.