Brown Mold grows in damp subterranean areas, and it grows by absorbing heat.
Creatures near brown mold take continuous cold damage from its heat-leeching effects.
Cold damage applied to the mold causes it to go dormant -- it stops absorbing heat for a brief period of time. Intense cold can even kill the mold.
Brown mold cannot be burned or lit aflame -- if exposed to flame, it instantly and hungrily grows in size, doubling, quadrupling, or more, depending on the intensity of the heat.