Fiendwurm (CR 28)

Gargantuan Magical Beast
Alignment: Always chaotic evil
Initiative: +5 (+1 Dex, +4 Improved Initiative); Senses: darkvision 60 ft., low-light vision, tremorsense, Listen +18, and Spot +17

AC: 27 (-4 size, +1 Dex, +20 natural), touch 7, flat-footed 26
Hit Dice: 24d10+216 (348 hp); DR: 15/-
Fort +23, Ref +15, Will +10
Speed: 60 ft., burrow 60 ft.
Space: 20 ft./10 ft.
Base Attack +24; Grapple +49
Attack: Bite +33 melee
Full Attack: Bite +33 melee
Damage: Bite 2d8+19
Special Attacks/Actions: Death rift, demonic belch, improved grab, swallow whole
Abilities: Str 36, Dex 13, Con 29, Int 7, Wis 14, Cha 8
Special Qualities: Acidic hide, acid immunity, portal
Feats: Alertness; Cleave; Dodge; Great Cleave; Improved Initiative; Improved Overrun; Mobility; Power Attack; Spring Attack
Skills: Listen +18 and Spot +17
Advancement: 25-72 HD (Colossal)
Climate/Terrain: Any desert, plains, and underground
Organization: Solitary or troupe (1 plus 2-8 dretches, quasits, or vrocks)
Treasure/Possessions: None

Source: Monster Manual II

Death Rift (Su): Upon its death, a fiendwurm's portal implodes. Every creature within 5 feet of the fiendwurm that fails a Reflex save (DC 31) is drawn into the collapsing portal and transported to the Abyss. The implosion destroys the fiendwurm's body along with the portal. Thus, any creatures transported to the Abyss via a death rift must find another means of returning to their original planes.

Demonic Belch (Su): Three times per day, a fiendwurm can use its connection with the Abyss to bring 1d4 demons to its aid. It expels these creatures from its mouth with a great belching sound. The demons arrive unharmed, but the fiendwurm's pain may cause it to attack them thereafter, if they seem to be easier prey than the opponents, or if there are no other creatures left to eat. Roll d% to determine the kind of demons that arrive: 01-50 jovocs, 51-75 quasits, 76-100 vrocks. These demons cannot use their summoning abilities for one hour after being snatched out of the Abyss. Once a fiendwurm uses this ability, it must wait 1d4 rounds before using it again.

Improved Grab (Ex): If a fiendwurm 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 +49). If it gets a hold, it can try to swallow the opponent in the next round. Alternatively, the fiendwurm has the option to conduct the grapple normally, or simply use its jaws to hold the opponent (-20 penalty on grapple check, but the fiendwurm is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals bite damage.

Swallow Whole (Ex): A fiendwurm can swallow a grabbed opponent that is at least two size categories smaller than itself by making a successful grapple check (grapple bonus +49). Once inside the fiendwurm, the opponent takes 2d8+13 points of bludgeoning damage and 1d8 points of acid damage per round from the creature's gizzard. A successful grapple check allows the swallowed creature to climb out of the gizzard and return to the fiendwurm's mouth, where another successful grapple check is needed to get free. Alternatively, a swallowed creature can try to cut its way out with either claws or a light piercing or slashing weapon. Dealing at least 25 points of damage to the gizzard (AC 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 opponent must cut its own way out. A Gargantuan fiendwurm's gizzard can hold 2 Huge, 8 Large, 32 Medium-size, or 128 Small or smaller creatures.

Acidic Hide (Ex): A fiendwurm produces a highly caustic mucus that coats its entire body. Touching its hide deals 3d6 points of acid damage to an organic creature or object, 5d8 points of acid damage to a metallic creature or object, or 1d10 points of acid damage to a stony creature (such as an earth elemental) or object. A gallon or more of water is needed to wash off the mucus.

Portal (Su): Lining the lowest part of the fiendwurm's gizzard is a portal to the Abyss that is activated by the presence of a living creature. A swallowed creature must make a Reflex save (DC 31) each round to avoid falling into or being squeezed through the portal. The Abyssal side of the portal is stationary, but the other side moves with the fiendwurm. If this portal is permanently closed, the fiendwurm instantly dies but does not implode.

Tremorsense (Ex): A fiendwurm can automatically sense the location of anything within 120 feet that is in contact with the ground.

A fiendwurm immediately lunges to bite and swallow any living creature it chances upon. If it seems to be overmatched, it uses its demonic belch ability to summon aid. A fiendwurm does not stop attacking until it is slain.