Purple worm

Gargantuan Magical Beast
Hit Dice: 16d10+112 (200 hp)
Initiative: –⁠2
Speed: 20 ft. (4 squares), burrow 20 ft., swim 10 ft.
Armor Class: 19 (–⁠4 size, –⁠2 Dex, +15 natural), touch 4, flat-footed 19
Base Attack/Grapple: +16/+40
Attack: Bite +25 melee (2d8+12)
Full Attack: Bite +25 melee (2d8+12) and sting +20 melee (2d6+6 plus poison)
Space/Reach: 20 ft./15 ft.
Special Attacks: Improved grab, swallow whole, poison
Special Qualities: Tremorsense 60 ft.
Saves: Fort +17, Ref +8, Will +4
Abilities: Str 35, Dex 6, Con 25, Int 1, Wis 8, Cha 8
Skills: Listen +18, Swim +20; racial bonuses
Feats: Awesome Blow, Cleave, Improved Bull Rush, Power Attack, Weapon Focus (bite), Weapon Focus (sting)
Environment: Underground
Organization: Solitary
Challenge Rating: 12
Treasure: No coins, 50% goods (stone only), no items
Alignment: Always neutral
Advancement: 16–32 HD (Gargantuan); 33–48 HD (Colossal)
Level Adjustment:

This creature looks like a massive worm covered with plates of dark purple, chitinous armor. Its toothy maw is as wide as a human is tall.

These massive scavengers attempt to consume any organic material they find. Purple worms are feared for swallowing their prey whole: Entire groups of adventurers have vanished down their gullets, one member after the other.

The body of a mature purple worm is 5 feet in diameter and 80 feet long, weighing about 40,000 pounds. The creature has a poisonous stinger in its tail.

A purple worm consumes great quantities of dirt and rock when tunneling. Its gizzard may hold gems and other acid-resistant items. In mineral-rich areas, purple worm castings might contain unrefined ores.

Combat

In battle, a purple worm forms into a coil 20 feet in diameter, biting and stinging anything within reach.

Improved Grab (Ex): To use this ability, a purple worm must hit with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can attempt to swallow the foe the following round.

Poison (Ex): Injury, Fortitude DC 25, initial damage 1d6 Str, secondary damage 2d6 Str. The save DC is Constitution-based.

Swallow Whole (Ex): A purple worm can try to swallow a grabbed opponent of a smaller size than itself by making a successful grapple check. Once inside, the opponent takes 2d8+12 points of crushing damage plus 8 points of acid damage per round from the worm’s gizzard (AC 17, 25 hp). See Swallow Whole for methods by which a swallowed creature may escape. A Gargantuan worm’s interior can hold 2 Large, 8 Medium, 32 Small, 128 Tiny, or 512 Diminutive or smaller opponents.

Skills: A purple worm has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.

Source: Monster Manual (version 3.5), page 211.