The following material is Open Game Content from the Menace Manual SRD
A neothelid is a 50-foot-long, wormlike creature with a mass of tentacles at one end. In the midst of this nest of tentacles is a toothy maw. The creature has no eyes or other sensory organs as such, though it unerringly senses the location of prey.
Blindsight (Ex): A neothelid is blind but can ascertain all creatures and objects within 500 feet by nonvisual means. Beyond that range, all targets have total concealment with respect to the neothelid.
Breath Weapon (Su): Once every 1d4 rounds, a neothelid can breathe a 50-foot cone of acid that deals 14d10 points of acid damage to every creature in its area. A successful Reflex save (DC 10 + 1/2 the neothelid’s Hit Dice + its Constitution modifier) halves the damage.
Damage Reduction 15/+2 (Su): A neothelid ignores the first 15 points of damage dealt by any weapon with a magical bonus lower than +2. In campaigns without magic weapons, the GM can either disregard the neothelid’s damage reduction or apply it only to certain types of weapons (ballistic, bludgeoning, piercing, slashing, or sonic/concussion).
Psionics (Sp): At will—charm person, clairaudience/ clairvoyance, detect thoughts, levitate, suggestion, telekinesis. Manifester level 10th; save DC 10 + neothelid’s key ability modifier + power level.
Improved Grab (Ex): To use this ability, the neothelid must hit a single opponent at least one size category smaller than itself with two tentacle rake attacks in the same round. If it gets a hold, it automatically deals damage for two tentacle rakes each round that the hold is maintained, and it can swallow in the next round.
Swallow Whole (Ex): If a neothelid begins its turn with an opponent two or more size categories smaller than itself held in its mouth, it can attempt a new grapple check as though trying to pin the opponent. If it succeeds, it swallows its opponent, automatically dealing bite damage. Once inside the neothelid, the opponent takes bludgeoning damage equal to the neothelid’s tentacle rake attack plus 1d6 points of acid damage per round from the monster’s gizzard.
A successful grapple check allows the swallowed creature to climb out of the gizzard and return to the neothelid’s maw, where another successful grapple check is needed to get free. Alternatively, the swallowed creature can attack from inside the gizzard using claws or a Small or Tiny slashing weapon. Dealing at least 25 points of damage to the gizzard (Defense 20) in this way creates an opening large enough to permit escape. Once a single swallowed creature exits, muscular action closes the hole; thus, another swallowed creature must cut its own way out. A Gargantuan neothelid’s gizzard can hold 2 Large, 8 Medium-size, 32 Small, or 128 Tiny or smaller opponents.
Neothelid: CR 18; Gargantuan aberration; HD 25d8+200; hp 312; Mas 27; Init +2; Spd 20 ft.; Defense 19, touch 4, flatfooted 19 (–4 size, –2 Dex, +15 natural); BAB +18; Grap +40; Atk +25 melee (2d6+10, tentacle rake); Full Atk +25 melee (2d6+10, 4 tentacle rakes); FS 20 ft. by 20 ft. (coiled); Reach 20 ft.; SQ blindsight 500 ft., breath weapon (DC 30), damage reduction 15/+2, improved grab, power resistance 25, psionics, swallow whole; AL evil; SV Fort +16, Ref +6, Will +16; AP 0; Rep +0; Str 30, Dex 7, Con 27, Int 16, Wis 15, Cha 9.
Skills: Climb +38, Listen +30, Swim +35.
Feats: Cleave, Improved Initiative, Power Attack, Sunder, Weapon Focus (tentacle rake).
Advancement: 26–45 HD (Colossal).