Here's a new one to keep you guys busy.
Mold Wyrm
This creature is a fungal behemoth created by leakage from the Basin of Boundless Life. It has both a passive and an active form.
In its passive state, the mold wyrm spreads out over a surface area roughly 60 feet in diameter, appearing as a continuous layer of grayish, scaly mold on the floor, walls, and ceiling of a tunnel or cavern. The resting mold wyrm simply covers up any nonambulatory natural molds and fungi already growing in the area it occupies. In this state, it always keeps a pile of jagged stones (usually obsidian) resembling a cairn somewhere on its thinly spread body.
When aroused by movement or vibration within its chamber, the fungus layer liquefies, flowing into a huge animate shape over the course of a single round. As it activates, it incorporates the jagged obsidian shards into its mouth to serve as teeth, placing them in several circular rows. In its fully active state, the mold wyrm appears as a mold-covered, gray-scaled worm with a huge, toothy maw, but no eyes and other sensory apparatus.
If the mold wyrm's bite attack exceeds the required "to hit" score by 4 or more against a size M or smaller target, the latter must make a successful saving throw vs. death magic or be swallowed whole. A swallowed victim suffers the effects of the spore cough (see below) every round while inside the mold wyrm (no saving throw). Those victims not immediately overcome may attempt to cut their way out with small slashing or piercing weapons such as daggers. Anyone who delivers 20 points of damage in this manner against the wyrm's AC 9 interior creates a slit large enough to permit escape at the beginning of the next round. Though the wyrm cannot swallow size L or larger creatures, this attack inflicts double normal damage against them.
Three times per day, the mold wyrm can cough forth a cloud of greenish-gray spores. Any nonvegetable creature within a 30 x 30 foot area must make a successful saving throw vs. death magic or cough for ld4+2 rounds, suffering ld6 points of damage per round and incurring a -2 penalty on all attack rolls, saving throws, ability checks, and proficiency checks until the coughing stops. A slow, poison, neutralize poison, or cure disease applied during this time dispels the coughing fit and prevents the infection that would (otherwise follow. Victims who stop coughing without benefit of healing magic have incorporated the mold wyrm spores into their own bodies. This infection suspends all natural healing and causes victims to become ravenous. If they do not eat double their normal rations each day, they begin to waste away, losing 10% of their original hit points each day. Though slow poison, neutralize poison, or cure disease can remove the affliction instantly, infected characters become very protective of the "warmth" they feel growing within, refusing all magical healing and escaping at the earliest opportunity from any companions who try to cure them. After ld6+6 days of infection, the victim's skin sloughs away, revealing a gelatinous mass of grayish mold that has replaced his or her internal organs. This goo splashes down like a column of viscous water to form a scaly mold layer covering a 30-foot-diameter area. The victim is now a brand-new mold wyrm with one-fourth of such a creature's normal Hit Dice. The new wyrm must rest for 8 hours before it can assume its active form.
Even with a successful saving throw against the spore cough, any creature within the spore cloud's area of effect breathes in a whiff of the disruptive spores and coughs violently, suffering the same damage and action penalty as those who failed their saving throws, but for only 1 round. They do not, however, become infected with spores. Vegetable- and fungus-based creatures (such as fungus hulks) that fail their saving throws suffer 1d10 points of damage from invading spores, but no infection.
Because of the trace of pure life-principle in the mold wyrm's body, it suffers only 50% of normal damage from physical attacks (including those of magic weapons) and can regenerate all lost hit points with 4 hours of rest in its passive state. The creature also has 10% magic resistance and is immune to sleep, charm, hold, and other mind-affecting spells.
Mold wyrms cannot remain active all the time, however. The creature must spend 8 out of every 24 hours resting in its passive state or begin losing 20% of its original hit points per hour. It can arrest this hit point loss at any time by resuming its passive state. While passive or shifting between states, the mold wyrm suffers double normal damage from damage-producing area effect spells. Attacks of any sort cause the creature to resume its active state immediately, regardless of the consequences.
Mold wyrm: AC 6; MV 9, burrow 9; HD 12, hp 60; THAC0 9; #AT 1 (bite); Dmg 4d4+4; SA swallow whole, spore cough; SD immunities, regeneration; SW rest, area effect spells; MR 10%; SZ G (25' long, 10' in diameter); ML steady (12); Int semi (4); AL N; XP 6,000.
Special Abilities: SA-swallows opponent whole with bite attack 4 or more greater than score needed to hit (save vs. death magic to avoid, 20 points of slashing or piercing damage against AC 9 to escape, spore cough automatically affects swallowed victims); spore cough (3/day) inflicts ld6 points of damage/round, penalizes attack rolls, saving throws, ability checks, and proficiency checks by -2 for ld4+2 rounds, and infects victim with spores (save vs. death magic drops duration to 1 round and prevents infection, infection negates natural healing and turns victim into quarter-strength mold wyrm in ld6+6 days if not cured, slow poison, neutralize poison, or cure disease removes infection); SD-half normal damage from physical attacks; immune to sleep, charm, hold, and other mind-affecting spells; regenerates all damage after 4 hours in passive state; SW-must rest 8 out of every 24 hours or lose 20% of original hit points/hour; double damage from damage producing area effect spells while passive or shifting states.
Originally appeared in Return to White Plume Mountain.