The stench of rotting meat accompanies this bloated, horse-sized worm.
Ghast Worm (CR 4)
N Large aberration Init +0; Senses darkvision 60 ft., tremorsense 60 ft.; Perception +10 Aura stench (10 ft. radius, DC 16, 1d6+4 minutes)
--- AC 18, touch 11, flat-footed 16 (+2 Dex, +7 natural, –1 size) hp 42 (5d8+20) Fort +7, Ref +3, Will +7 Immune disease, poison
--- Speed 30 ft., burrow 20 ft. Melee bite +7 (1d8+6 plus disease and grab and paralysis) Space 10 ft.; Reach 5 ft. Special Attacks paralysis (1d4+1 rounds, DC 16), spit entrails, swallow whole (1d4 acid plus disease and paralysis, AC 13, 4 hp)
--- Str 18, Dex 15, Con 19, Int 2, Wis 15, Cha 10 Base Atk +3; CMB +8 (+12 grapple); CMD 20 (28 vs. trip) Feats Skill Focus (Perception), Great Fortitude, Weapon Focus (bite) Skills Climb +10, Perception +10 SQ stench of undeath
--- Environment any underground Organization solitary, pair, or nest (3–6) Treasure incidental
--- Disease (Su) Ghoul Fever: Bite, spit entrails, and swallow whole—injury; save Fort DC 16; onset 1 day; frequency 1/day; effect 1d3 Con and 1d3 Dex damage; cure 2 consecutive saves. The save DC is Constitution-based. A humanoid who dies of ghoul fever rises as a ghoul at the next midnight. A humanoid who becomes a ghoul in this way retains none of the abilities it possessed in life. It is not under the control of any other creature, and behaves like a normal ghoul in all respects. A humanoid of 4 Hit Dice or more instead rises as a ghast. Spit Entrails (Ex) Once every 6 hours, a ghast worm can violently invert itself, spitting its internal organs out of its mouth, filling a 15-foot cone. Doing so does not harm the ghast worm, but allows it to make one combat maneuver check against each creature inside the affected cone. For each of these creatures, if the ghast worm's check exceeds that creature's CMD, that creature takes 1d4 points of acid damage and is exposed to the ghast worm's disease and paralysis abilities. Using the spit entrails attack immediately releases any creature the ghast worm has swallowed whole. The ghast worm's internal organs immediately return to their proper place once the attack is resolved. Stench of Undeath (Ex) Undead creatures react to a ghast worm as if it were an undead creature instead of a living creature. This doesn't guarantee that undead will do anything to assist a ghast worm, but undead that hate, target, or feed upon the living typically ignore ghast worms.
A ghast worm is descended from normal vermin that fed upon filth that was never meant to be consumed: the corpses of alien gods, the flesh of the undead, other aberrant substances better left unmentioned. Whatever the exact source of a given ghast worm's ancestral corruption, the worm is a creature of monstrous size and countenance, spreading disease and undeath in its wake.
Despite the taint often left in its wake, a ghast worm is not gratuitously destructive, lacking the necessary intelligence to actively engage in evil. For the most part, the ghast worm is a bestial hunter and scavenger, driven by hunger to find or generate corpses upon which feed. Though their corrupted flesh sets them apart from nature, ghast worms lead lives very much like those of ordinary animals.
Undead tend to view ghast worms as either distant kin or vermin beneath notice, ignoring any ghast worms that are not actively interfering in their affairs. Druids, meanwhile, tend to loath ghast worms, characterizing them as unnatural parasites in flesh of the earth. While this may be hyperbole on the part of druids, there is no denying the fact that ghast worms have a tendency to pollute and disrupt the ecosystems that support their voracious appetites.
Conqueror Worm (CR 5) It is not unheard of for ghast worms to spontaneously rise as undead within 1d4 days of their demise. A conqueror worm, named for its victory over death, is a typical example of an undead ghast worm; it is a ghast worm with the ju-ju zombie template. Undead ghast worms are no more intelligent than their living kin, and retain the appetite for dead flesh that they possessed when they were living creatures.