Purple Worm (CR 12)

Gargantuan Magical Beast
Alignment: Always neutral
Initiative: -2 (Dex); Senses: tremorsense 60 ft. and Listen +18


AC: 19 (-4 size, -2 Dex, +15 natural), touch 4, flat-footed 19
Hit Dice: 16d10+112 (200 hp)
Fort +17, Ref +8, Will +4
Speed: 20 ft., burrow 20 ft., swim 10 ft.
Space: 20 ft./ 15 ft.
Base Attack +16; Grapple +40
Attack: Bite +25 melee
Full Attack: Bite +25 melee and sting +20 melee
Damage: Bite 2d8+12, sting 2d6+6 and poison
Special Attacks/Actions: Improved grab, swallow whole, poison
Abilities: Str 35, Dex 6, Con 25, Int 1, Wis 8, Cha 8
Special Qualities:
Feats: Awesome Blow; Cleave; Improved Bull Rush; Power Attack; Weapon Focus (bite); Weapon Focus (sting)
Skills: Listen +18 and Swim +20
Advancement: 16-32 HD (Gargantuan); 33-48 HD (Colossal)
Climate/Terrain: Underground
Organization: Solitary
Treasure: No coins, 50% goods (stone only), no items

Source: Monster Manual

Combat

In battle, a purple worm forms into a coil 15 feet across, biting and stinging anything within reach.

Improved Grab (Ex): To use this ability, the purple worm must hit with its bite attack If it gets a hold, it automatically deals bite damage and can attempt to swallow the foe.

Swallow Whole (Ex): A purple worm can try to swallow a grabbed opponent of Large or smaller size by making a successful grapple check. Once inside, the opponent takes 2d8+12 points crushing damage plus 1d8 points of acid damage per round from the worm's gizzard. A swallowed creature can climb out of the gizzard with a successful grapple check. This returns it to the worm's maw, where another successful grapple check is needed to get free. A swallowed creature can also cut its way out by using claws or a Small or Tiny slashing weapon to deal 25 points of damage to the gizzard (AC 20). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out.

The worm's interior can hold two Large, four Small, eight Tiny, sixteen Diminutive, or thirty-two Fine or smaller opponents.

Poison (Ex): Sting, Fortitude save (DC 24; initial damage 1d6 temporary Strength, secondary damage 2d6 temporary Strength.

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