Nimergan grew in irregular patches 8‒12 ft (2.4‒3.7 m) in diameter and only 1‒3 in (2.5‒7.6 cm) tall. It resembled a beige, frayed umbrella with dark brown bumps on the stem.
Mature nimergan was sealed into a cask to die. The brown bumps were actually a parasitic fungus that fed upon the stem and fermented into a potent alcohol that could be consumed. Nimergan that was allowed to ferment too long could actually form an alcohol so potent that it could kill.
Duergar were especially fond of the drink, which was also known as nimergan. They were known to challenge outsiders to a drinking contest of the more potent version of the alcohol. Being more resistant to its effects, the duergar, more often than not, watched as their opponent went into a coma and sometimes died from over-indulgence.