Onyx Worm (CR 14)

Huge Magical Beast (Psionic)
Alignment: Usually neutral
Initiative: +0; Senses: darkvision 60 ft., low-light vision, tremorsense, Listen +5, and Spot +3


AC: 18 (-2 size, +10 natural), touch 8, flat-footed 18
Hit Dice: 14d10+70 (147 hp); DR: 15/iron
Fort +14, Ref +9, Will +4
Speed: 20 ft., burrow 20 ft.
Space: 40 ft./10 ft.
Base Attack +14; Grapple +18
Attack: 2 slams +16 melee
Full Attack: 2 slams +16 melee
Damage: Slam 4d6+8
Special Attacks/Actions: Breath weapon, psionics, sonic blast
Abilities: Str 26, Dex 10, Con 20, Int 3, Wis 11, Cha 5
Special Qualities: death throes
Feats: Psychic Bastion (x3) (B)
Skills: Listen +5 and Spot +3
Advancement: 15-21 HD (Huge); 22-42 HD (Gargantuan)
Climate/Terrain: Any land and underground
Organization: Solitary
Treasure: None

Source: Web

Combat

Onyx worms are relentless in combat, and they pulverize their foes with their body and constant mental and sonic assault. While they usually use their psionic abilities for movement and borrowing purposes, some have even been known to use them in combat, as well.

Breath Weapon (Su): Once per hour, an onyx worm can release a sonic energy attack in a cone shape similar to a breath weapon. The cone has a length of 80 feet and causes 15d6 points of damage (Reflex half DC 22). Creatures in the area of effect of the breath weapon are also psionically assaulted by a mind blast (psionic combat mode); psionic creatures can defend as normal. An onyx worm is immune to its own breath weapon.

Psionics (Sp): At will -- body equilibrium, levitate, improved telekinesis, true metabolism; these abilities are as the powers manifested by a 18th-level psion.

Attack/Defense Modes (Sp): At will -- mind blast*, mind thrust*/intellect fortress. An onyx worm's mind blast attack is part of its breath weapon. Mind thrust is part of its sonic blast and death throes. The area of effect of these attack modes is the same as the attack instead of that as listed in the Psionics Handbook. The creature can use these attack modes only in conjunction with the listed abilities.

Sonic Blast (Su): Once per round, an onyx worm can release a blast of sonic energy that affects all creatures within 20 feet for 3d6 points of damage (Reflex half DC 22). This blast can be delayed. If delayed, the blast becomes more intense and increases by 3d6+3 points of damage per round. It also expands in size by a 10-foot radius per round. The blast can go up to a maximum of 12d6+9 points of damage and a 50-foot radius. Creatures in the area of effect of the blast are also psionically assaulted by a mind thrust (psionic combat mode); psionic creatures can defend as normal.

Death Throes (Ex): When killed, an onyx worm explodes with one final sonic-based explosion that sends shards of crystal in all directions. The explosion deals 12d6 points of sonic damage and 8d6 points of piercing damage to everything within 60 feet (Reflex half DC 22). Creatures in the area of effect of the explosion are also psionically assaulted by a mind thrust (psionic combat mode); psionic creatures can defend as normal. The crystal shards have no value but are often mistaken for onyx.

Tremorsense (Ex): An onyx worm can automatically sense the location of anything within 60 feet that is in contact with the ground.