Tunnel Terror (CR 15)

Huge Aberration
Alignment: Always neutral evil
Initiative: +6 (+2 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., tremorsense 60 ft., Listen +11, and Spot +11

AC: 18 (-2 size, +2 Dex, +8 natural), touch 10, flat-footed 16
Hit Dice: 15d8+90 (171 hp)
Fort +13, Ref +10, Will +12
Speed: 20 ft., climb 10 ft.
Space: 15 ft./10 ft.
Base Attack +13; Grapple +30
Attack: Tentacle slap +20 melee
Full Attack: 2 tentacle slaps +20 melee
Damage: Tentacle slap 1d8+9
Special Attacks/Actions: Engulf, psionics, suffocating constriction 1d8+10
Abilities: Str 28, Dex 15, Con 20, Int 11, Wis 13, Cha 16
Special Qualities: Camouflage
Feats: Alertness; Great Fortitude; Improved Initiative; Lightning Reflexes; Power Attack; Skill Focus (Hide); Skill Focus (Move Silently)
Skills: Climb +17, Hide +10, Listen +11, Move Silently +12, and Spot +11
Advancement: 19-32 HD (Huge); 33-54 HD (Gargantuan)
Climate/Terrain: Any underground
Organization: Solitary or pair
Treasure/Possessions: -

Source: Fiend Folio

Engulf (Ex): A tunnel terror can engulf one Large or smaller foe that has stepped into its body by making a successful grapple attempt against its foe. This move does not provoke an attack of opportunity. Engulfed victims are entangled and automatically take damage from suffocating constriction (see below). If the tunnel terror gets a hold, it is free to use its tentacles to strike at other targets while it constricts. Attacks made on an engulfing tunnel terror deal half their damage to the monster and half to the trapped victim.

Psionics (Sp): At will - arcane eye, bull's strength, cat's grace, endurance, prying eyes, stone shape, telekinesis, wall of stone. Caster level 12th; save DC 13 + spell level.

Suffocating Constriction (Ex): An engulfed creature takes 1d8+13 points of bludgeoning damage, has no air to breathe, and begins to suffocate.

Camouflage (Su): Since a tunnel terror looks like a part of the tunnel when at rest, it takes a successful Spot check (DC 20) to notice it before it attacks. Dwarves can use stonecunning to notice a tunnel terror.

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

Skills: Tunnel terrors have a +8 racial bonus on Climb checks and can always choose to take 10 on Climb checks, even if rushed or threatened.