What's growing in the dark corners of your fantasy world? Here are sixteen fantastic fungi to fascinate, confuse, and trouble adventurers in dungeon and wilderness. Some may have uses in magic and alchemy, though for the most part that's left to the DM's discretion.
Goblin's lantern: A pale mushroom with a thick stalk and bell-shaped cap that emits a bluish phosphorescence in a 5' radius. It grows mainly in dark, gloomy forests on decaying wood. They may be picked and will continue to shed light for 1d4 days. Mildly toxic, goblin's lantern causes painful gastric distress for 1d4 hours if eaten.
Corpsepyre: Another luminous fungus, this mold glows with an orange or red light. It grows only on decaying flesh, giving it the appearance of a bed of burning embers. It has no nutritional value, but is otherwise harmless, though few would care to eat mold scraped off a corpse.
Ratbane: This nuisance looks like tiny blue-black nubs or domes, about the size of peas, growing very closely together over an area of dungeon floor or wall. Each fungus secretes a strong adhesive substance which can trap small creatures such as bats and rodents. Trapped victims die and decompose, feeding the fungus. Larger creatures are slowed to 1/4 of their normal movement if they try to walk across a patch of ratbane. Only the very foolish would try to eat this fungus; doing so quickly clogs the mouth and throat, resulting in death by asphyxiation.
Miner's muffin: A puffy, spongy round mushroom, usually yellow to beige in color. It grows in caves and dungeons of sedimentary rock, usually in patches of 2-16 mushrooms. Miner's muffin is edible and nutritious, if a bit bland. Four mushrooms are equivalent to a full day's rations.
Fool's glory: A large mushroom with a broad, flat cap of royal purple atop a white stalk. So named for its powerful hallucinogenic properties, which typically produce extreme feelings of euphoria, fearlessness, and invincibility, and possibly delusions of superhuman powers such as flight or immunity to fire. Sadly, it confers no actual benefits on the imbiber other than a temporary imperviousness to pain.
Bleeding wall fungus: This gelatinous, translucent, irregularly-shaped fungal mass is a deep crimson in color, and typically grows in the mortared joints of brick or stone walls. Despite its horrific appearance, bleeding wall fungus is edible and tasty, with a curious spicy flavor.
Ogre's toes: Very large puffball-like fungi, ruddy brown in color, that grow in rows of 3-8. All in one row are fruiting bodies of the same fungal mass, which sprout one at a time in linear order so that they tend to be arranged neatly by descending size and resemble the toes of a monstrous foot poking up through the soil. Ogre's toes are deadly poisonous. Anyone eating even a small piece must save vs. poison or suffer 1d8 turns of excruciating spasms and muscle paralysis culminating in death from heart failure.
Slickwort: This thin, blue-green mat is actually a colony of fungi that grows on stone floors. The colony secretes a greasy, slippery substance that makes footing in that area highly uncertain. A floor covered with slickwort may be traversed safely at half normal movement rate; faster movement, or stepping onto it unaware requires a d20 check against Dexterity to avoid falling. Intelligent dungeon-dwelling monsters sometimes cultivate patches of slickwort, either as traps or to enhance the effectiveness of physical traps such as pits and slides.
Glass toadstool: These very rare medium to large mushrooms grow in places with an abundance of silica, which they incorporate into their structures to give them strength and rigidity. In their natural state, glass toadstools look much like ordinary mushrooms, though shifting or flickering light causes the surface to sparkle. They may be of almost any color, depending on other minerals present in their environment. When stepped on or crushed, a glass toadstool crunches rather than squishes. If picked, and the organic parts dissolved with acid or allowed to rot away, the exquisite, lacy form of the toadstool's silica "skeleton" remains, and may be worth anywhere from 5-200 gp depending on size, color, and perfection.
Firemoss: Actually a lush, feathery, yellow-orange mold, firemoss grows where sulfur is plentiful. Part of its name is accurate, however: firemoss is quite flammable, a torch or even a spark that comes into contact with it causes it to combust in a quick burst of flame, leaving behind the pungent scent of brimstone. A character or creature caught in the middle of a patch of firemoss when it burns take 1d4 damage.
Cryomyceum: This strange, pale blue, semi-magical mold requires large amounts of heat energy to grow. In cool environments it can lay dormant for years. When it comes in contact with a heat source, its cells awaken and begin to absorb heat and multiply. The mold is cold to the touch, like ice, but not extreme enough to cause damage from brief contact. Spending a night in a cavern full of the stuff may cause harm or even death from hypothermia, however. Some clans of dwarves are known to use crymyceum mold to chill foodstuffs for long-term storage. While the mold thrives on warmth, extreme heat such as flame cooks and kills it.
Sorcerer's cap: A deep blue mushroom with a thin stalk and a tall, conical cap, sorcerer's cap thrives near the edges of stagnant, peaty ponds. When mature, its blue color is spangled with tiny white spots. Sorcerer's cap is prized by mages and scholars for its virtues of mind and memory enhancement. Consuming a mature cap grants a bonus of +1 to Intelligence for 1d6 hours. It also has the strange side effect of causing rapid growth of head and facial hair, about two inches per hour, giving the eater a wizardly mane and beard.
Witch's spy: These disturbing but harmless fungi are spherical and white veined with red, except for a large spot of blue, green, or umber, giving them the appearance of eyeballs growing from the wall of a cave or the trunk of a dead tree.
Grave ghost: Tall, lumpy, and nearly translucent white mushrooms that often grow in circles similar to fairy rings. According to folk superstition, they spring up in old burial sites, especially unmarked or unconsecrated graves, and keep the spirits of the unfortunate folk buried there at rest. They are extremely poisonous, requiring a save to avoid death within seconds. Evil folk sometimes extract the poison for nefarious purposes, and the mushroom is reputed to have magical properties for spiritual and necromantic purposes as well.
Pyromycofusium: A small, fiery red mushroom, pyromycofusium grows only on the corpses of red dragons and other creatures with a similarly close affinity for fire. As the body decomposes, the mushroom takes up the fiery essence of the creature. Striking or crushing the mushroom causes it to burst into a small and brief but intense conflagration lasting 1d4 rounds. A creature unfortunate enough to be in contact with the mushroom when that happens takes 1d8 points of damage each round, with a cumulative 5% chance per point of damage of any combustible materials on his person catching fire too. With great caution, pyromycofusium may be dried and ground to powder, which can be used for fireworks and magical and alchemical purposes. Dwarven master smiths sometimes use small amounts of the powder for welding and cutting metals.
Pixie's goblets: These slender, graceful pale lavender mushrooms have concave tops. Folklore has it that drinking the morning's dew from one will grant the drinker the ability to see invisible fairies and elementals. Its spores are known to be potent soporifics, but are difficult to gather in sufficient quantities.