Tunnelmouth Dweller

This deep brown beast is half mouth: its jaws are ten feet across, the width of a typical dungeon passage. Two great blind orbs sit just beside the lips, milky white leftovers from eyed ancestors. The creature now navigates purely by echolocation.

A dweller has a single attack, and it rarely needs another. It surges forward and engulfs anything up to Size H, its elastic hide letting it take in prey as large as itself. Three adventurers fit easily, four if they are bunched in a tight formation such as a spear line. The long teeth deal 2d8 damage to everyone swallowed in the first round, and after that digestive fluids eat away 1d6 points per round until the victim dies or is cut free.

Characters have two ways to stay out of the gullet. One is to dodge the lunge. The other is to jam the jaws open with a pole or polearm at least 10 feet long, which takes a successful Dexterity check and only works if the weapon is already in hand. Once inside, only short stabbing weapons such as daggers, knives or short swords can be used.

Thick slime coats the whole mouth and throat. It snuffs torches and open lantern flames, completely smothers any mundane fire aimed into the maw, and cuts magical fire to half damage, or one quarter if the dweller passes its saving throw. This protection covers only the front of the beast. Fire striking its flank or tail works as normal, but since the body plugs the corridor wall to wall, reaching those angles is a challenge in itself.

Dwellers hunt alone. Once a year a pair meets for about an hour to mate and parts peacefully, but if they meet again before the next season, even that afternoon, each tries to eat the other. Woe to a party caught between two in a corridor with no side passages. A female lays six leathery eggs, and usually only one or two of the young survive to maturity.

Wizards prize the stretchy hide as a component for a bag of holding. The mucus is bottled as a fire suppressant and fetches about 50 gp per vial, each vial enough to put out one torch, lantern or campfire. The creature hoards nothing, but it eats plenty of well-equipped adventurers, so anyone wanting their gear must either carve up the corpse or sift through its dung.

Gullible buyers pay 500 gp per egg and regret it. A hatchling is 2 feet long with 2 Hit Dice, and it adds two Hit Dice and a little over 2 feet of length every month, reaching adult size in 8 months. Its hunger makes it a costly guardian that even evil masters tire of within weeks.