Brown Mold

What Is Brown Mold?

Brown mold is a dangerous dungeon growth that feeds on heat rather than flesh. At a distance it may resemble ordinary mildew, but its feeding leaves a chill in the surrounding air. A living creature that approaches closely may suffer a sudden loss of warmth before touching it. Its danger is geographical: the patch does not pursue intruders, but its position can make a door, narrow passage or treasure chest difficult to reach.

A common mistake is to treat the growth like an infestation that ought to be burned away. Fire feeds its expansion. Cold is the effective answer, and a party that notices the chill before lighting a torch or casting a fire spell has a chance to solve the problem without suffering it.

Brown mold should be run as an environmental hazard, not as a monster with invented Armor Class, Hit Points, actions or ability scores. Its Challenge Rating in Pathfinder and D&D 3.5e is a hazard rating; modern editions use their own hazard procedures.

Brown Mold Rules by Edition

Select the ruleset used at your table. Although each edition describes the same heat-draining growth, the sizes, injury rules and hazard classifications are not interchangeable.

What Changed Between Editions?

Across all four editions: The chill extends farther than the damage, a torch is hazardous rather than helpful, and damaging cold destroys the growth. The editions’ numbers must not be combined.

Running Brown Mold at the Table

Give the players a warning

Start with an unseasonable draught, moisture frozen around a hinge, or a cold strip along the flagstones. The frost signals that something is wrong before characters reach the five-foot danger zone. A character who studies the surface can recognise that the chill is centred on the brown growth.

Let their equipment matter

A torch carried into the danger zone may turn one patch into a larger obstruction. A player who extinguishes the flame, backs out of the room, sends a cold effect from a safe distance or takes an alternate route has solved a meaningful problem. Ordinary physical separation from the affected area is effective; an ingenious plan need not be reduced to a compulsory tools check.

Use the room, not just the damage

Place the growth where its spreading footprint changes choices: beneath a winch, over a stairwell landing, behind a locked grate or inside a chest that has already acquired a layer of frost. A hazard placed in empty ground is simply avoided; one next to a needed mechanism demands thought.

Ready-to-Run Encounter: The Brewer’s Cold Cellar

A castle brewer has locked the doors of a subterranean store. Two servants sent to fetch winter ale have returned shivering and empty-handed. The steward needs the cellar opened before a visiting lord’s feast, but fears losing more staff. Beyond the door is a damp stone chamber where a ring of frost surrounds an ale rack. A brown growth clings to the wood around the only winch that opens the inner delivery gate.

Difficulty: Use the hazard’s printed edition statistics above. The people, setting and deadline in this example are original encounter material, not a published trap stat block.

Folklore and Historical Inspiration

Dark cellars, damp food stores and underground passages naturally suggest unseen danger. Actual fungi colonise surfaces through biological growth; they do not magically consume heat, inflict freezing injuries at a distance, or multiply when presented with fire. Brown mold turns the familiar sight of cellar mildew into an impossible predator. The distinction keeps the imagined hazard vivid without treating it as real history.

For a grounded visual starting point, consider cellar moulds recorded in European wine stores. In a medieval dungeon, the supernatural counterpart can betray itself through frost around jars and barrels, chilled mortar, or the absence of insects near an affected wall.

Common Questions

Is brown mold a monster?

No. It is a stationary dungeon hazard, and its original Challenge Rating is not a creature stat block. It has no initiative, attacks or treasure of its own.

Does fire kill it?

No. All four editions make fire a cause of expansion. Use a cold-damaging effect to destroy a patch.

Does the 30-foot chill cause damage?

No. Thirty feet describes the warning chill. The harmful zone is within five feet of the growth, using the chosen edition’s timing.

Are Pathfinder and fifth-edition damage interchangeable?

No. Pathfinder 1e and D&D 3.5e use nonlethal cold damage and a CR 2 hazard. The two fifth-edition treatments use a Constitution save against 4d10 Cold damage.

Can thieves’ tools disarm brown mold?

Not as an ordinary mechanical device. Tools may open or jam a box containing the mold; the organism itself is defeated through distance, temperature-based counterplay or avoiding its reach.

Related Entries and Rules Sources

• Traps — design, detection and the Box of Brown Mold
• Yellow Mold — a very different fungal danger
• Cone of Cold — one method of destroying brown mold
• Bestiary — other creatures and hazards
• D&D 2024 Brown Mold reference
• D&D Dungeon Master’s Guide (2014)
• Pathfinder 1e Environmental Hazards
• D&D 3.5e Dungeon Terrain SRD

Rules acknowledgement: The Pathfinder 1e and D&D 3.5e treatments follow their respective open rules references. The 2014 and 2024 hazard summaries are separately paraphrased for table use; D&D 2024’s classification is a hazard severity, not a Challenge Rating. Encounter descriptions and advice are original setting material.