Lucent Worm (CR 17)

Gargantuan Magical Beast
Alignment: Always neutral
Initiative: +3; Senses: darkvision 60 ft., low-light vision, and tremorsense 60 ft.

AC: 23 (-4 size, -1 Dex, +18 natural), touch 5, flat-footed 23
Hit Dice: 22d10+154 (275 hp); DR: 15/magic piercing or slashing
Fort +20, Ref +12, Will +7
Speed: 40 ft., burrow 30 ft., swim 30 ft.
Space: 20 ft. (coiled)/15 ft.
Base Attack +22; Grapple +46
Attack: Bite +31 melee
Full Attack: Bite +31 melee
Damage: Bite 2d8+12/19-20 plus paralysis
Special Attacks/Actions: Crush, improved grab, paralysis, swallow whole
Abilities: Str 34, Dex 9, Con 251, Int 10, Wis 8, Cha -
Special Qualities:
Feats: Blind-fight; Cleave; Combat Reflexes; Great Cleave; Improved Critical (bite); Improved Initiative; Power Attack; Weapon Focus (bite)
Skills: Hide +12 and Swim +20
Advancement: 23-32 HD (Gargantuan); 33-55 HD (Colossal)
Climate/Terrain: Any aquatic, mountain, or underground
Organization: Solitary
Treasure/Possessions: Standard

Source: Fiend Folio

Crush (Ex): A lucent worm can move over opponents three or more size categories smaller than itself as a standard action, using its whole body to crush them. A crush attack affects as many creatures as can fit under the lucent worm's body. Each creature in the affected area must succeed on a Reflex save (DC 33) or be pinned, automatically taking 4d6+13 points of bludgeoning damage. Thereafter, if the lucent worm chooses to maintain the pin, treat it as a normal grapple attack (grapple bonus +46). While pinned, the opponent takes crush damage each round.

Improved Grab (Ex): If a lucent worm hits an opponent that is at least one size category smaller than itself with a bite attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +46). If it gets a hold, it can swallow the opponent on its next successful grapple check. Thereafter, the lucent worm has the option to conduct the grapple normally, or simply use its bite to hold the opponent (-20 penalty on grapple check, but the lucent worm is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals bite damage.

Paralysis (Ex): Any creature hit by a lucent worm's bite or crush attack must make a Fortitude save (DC 28) or be paralyzed for 4 rounds.

Swallow Whole (Ex): A lucent worm can swallow a single creature that is at least two size categories smaller than itself by making a successful grapple check (grapple bonus +46), provided it already has that opponent in its maw (see Improved Grab, above). Once inside the lucent worm, the opponent takes 2d8+12 points of bludgeoning damage and 2d4 points of acid damage per round from the lucent worm's stomach. A successful grapple check allows the swallowed creature to climb out of the stomach and return to the lucent worm's maw, from where another successful grapple check is needed to get free. Alternatively, a swallowed creature can try to cut its way our with either claws or a light piercing or slashing weapon. Dealing a total of at least 30 points of damage to the stomach (AC 19) 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 opponent must cut its own way out. A lucent worm's maw can hold 2 Large, 4 Medium-size, or 16 Small or smaller opponents.

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

Skills: Lucent worms have a +15 racial bonus on Hide checks. Lucent worms have a +8 racial bonus on any Swim check to perform some special action or avoid a hazard and can always choose to take 10 on Swim checks, even if distracted or endangered.

When confronted with prey, which is any living creature, a lucent worm attacks with its bite. If confronted with multiple foes, it typically attempts a crush attack before engaging remaining opponents with its bite.