Worm [Mystara]

Several kinds of huge, crawling invertebrates resembling giant caterpillars or earthworms inhabit this world. Most swallow prey whole; swallowed victims fight at -4 to hit and +4 on initiative, and need a slashing weapon to cut free.

Great annelid: usually a full thousand feet in length and 25 across, with rare giants of 2,000 by 40. Its segmented, gray-brown hide looks like wet stone, and its funnel mouth holds three rows of teeth. It bores through bedrock almost as fast as it crawls and, mindless rather than predatory, tries to eat anything it meets, swallowing up to huge creatures on a bite 5 or more above the number it needs and flinging them 3d10 feet down its throat. The grit-packed gullet deals 2d6+6 acid and abrasion per round (2d6 if immune to acid) and prevents spellcasting; escape takes 25 damage to one spot against AC 5. Heat and pressure cannot harm it. At egg-laying time this hermaphrodite sends a false lure, perhaps mimicking a rich cache of gems, that draws earth elementals, xorn and kin; its bite permanently paralyzes any elemental creature failing a save vs. paralyzation, and it lays eggs on the body. It lives anywhere underground, even in lava, but avoids water. Miners prize its tunnels yet dread it, for one can eat a rich vein in minutes.

Caecillia: a gray worm that is little more than a giant fanged mouth, hiding under loose soil to ambush passersby. An unadjusted 19 or 20 swallows a large or smaller target for 1d8 per round. The tight gullet stops anyone drawing a weapon, so only a victim already holding a small blade can cut out, needing 10 damage against AC 9. It holds one large, two man-sized, four small or eight tiny creatures, and once full it retreats to digest.

Fyrsnaca: the adult red worm, distant kin to purple worms, smooth reddish purple with a hot-iron glow in its toothy maw. It eats minerals, not flesh, but attacks intruders who do not retreat quickly or toss it a gem or some precious metal; through speak with monsters it might even hire out for ample payment in such treasures. Every 1d3 rounds it breathes fire in a 50-foot line, 5 feet across, for 2d6 (save vs. breath weapon for half). Now and then its inner heat flares and it disgorges 2d6 red worms, then must submerge in water or burn up, lying dormant 50 years. Disturbed, it fights fearlessly (morale 20) but never leaves the water.

Red worm: the fyrsnaca's larva, with translucent red skin showing its organs. These ravenous carnivores sense vibration and burst out of solid rock (foes -3 on surprise). They breathe no fire, but a bitten creature that fails a save vs. poison takes double bite damage.

Leviathan: among the mightiest beings on the Prime Material. Desert leviathans are eyeless, sand-colored, 500 feet long and 40 wide; marine ones are sleeker, 650 feet long, with huge eyes for the deep. They attack any sizable creature moving within a quarter mile, a wave rising in sand or sea as they approach, and gulp a whole block of terrain: 30 feet on a side of sand, or 50 of seawater. Everyone in it saves vs. breath weapon at -4 or is swallowed (helpless creatures get no save), taking bite damage (3d12 desert, 4d10 marine) plus 4d12 from digestion, or 2d12 if acid resistant. Escape takes 50 damage against AC 5, and anything undigested after a turn is spat out. Leviathans ignore poison, disintegration and any non-damaging spell, magic or psionic effect, and halve all other damage. A marine leviathan swimming in a tight loop for three rounds raises a whirlpool 200 feet deep, narrowing from 100 feet across to 50, that drags everything down to it while it swims and one round after.

Slime worm: a pale gray worm whose sticky back collects coins and trinkets until it resembles a treasure heap; only 15% of onlookers spot the ruse. It ambushes unaware prey, swallowing up to large targets on an unadjusted 18 or more (always on a 20) for 2d6 per round. As with the caecillia, only a victim already holding a small blade can escape, with 10 damage against AC 8, and its gullet has the same capacity, but a full slime worm keeps fighting without swallowing more.