Brown mold

Brown mold is a fungus that saps heat from its surrounding environment and creatures.

Properties
Brown mold typically grows in patches covering up to ten square feet. It feeds on warmth, drawing heat from its surroundings, causing the temperature around it to be frigid, regardless of the climate. Creatures within 5 feet of a brown mold patch must make a DC 12 Constitution save, taking 4d10 cold damage on a failure and half as much on a success.

Brown mold is immune to fire, and sources of fire within 5 feet of a patch cause the mold to grow and expand in the fire's direction. Inversely, brown mold exposed to cold damaging effects is destroyed.

History
The Mighty Nein encountered patches of brown mold while exploring the Tombtakers secret entrance to the ruins of Aeor. Caduceus Clay was able to identify the mold, and Essek Thelyss, who was accompanying them, used his Ray of Frost cantrip to destroy patches of it to ease their navigation through the ruined tunnels.