Brown mold

Brown mold was a fungus that grew in response to warm. So extremely did it absorb heat that it produced an area of cold around it.

Description
Brown mold often grew in subterranean or dungeon environments in large patches of about five feet (one and a half meters) in diameter. A patch of this size absorbed enough heat to cool the temperature of the air within a 30-foot (nine meter) radius. Within five feet (one and a half meters) of the patch of mold, it was cold enough to cause non-lethal injury to some creatures.

Brown mold grew extremely quickly when exposed to great sources of heat such as a nearby flame, doubling in size in only a matter of seconds. In contrast, the mold could be annihilated almost immediately by the effects of a spell dealing cold damage

Usage
Besides its natural existence as a dungeon hazard, some found practical uses for brown mold, such as using it to cool food pantries, as was done in the Cathedral of Emerald Scales in Hlondeth.

Brown mold was also created by the spell mold touch, which was a unique spell available to followers of nature deities Eldath, Mielikki, and Silvanus.

Rumors
The mind flayers were rumored to have developed varieties of brown mold that continued to cool the vicinity around them without harming other life. These varieties were said to grow on illithid homeworlds.