Timmask was a squat toadstool that grew to a width and height of about two feet (60 centimeters) and occurred in small numbers, usually no more than four in a cluster. It had a beige-colored cap that was crossed with red and orange stripes. If it was heavily damaged or killed by uprooting, it spewed a cloud of spores out to a radius of 15 ft (4.6 m). All those within the cloud were poisoned for about a minute unless their constitution was sufficient to shake off the effects of the spores. Those who failed to resist acted like they were under the influence of a confusion spell until it wore off.
Many creatures from the lower planes found timmask to be a delicacy, especially tanar'ri. The fungus could be used as a material component in the summoning of demons and/or offered as an enticement—both uses increased the likelihood of success. Timmask could also enhance necromancy spells, slightly increasing their effectiveness and doubling their duration (where applicable). A whole, intact mushroom sold for 5,000 to 8,000 gold pieces in the Underdark. Prices on the surface were twice as high. When ground into powder, a single timmask produced enough substance to be used in 21–30 spells. In this form, a sealed jar of timmask powder, enough for five spells, sold for 150 gp.