Araumycos

Araumycos (Dwarvish for "Great Fungus") was an enormous fungal growth that lived in the Upper Northdark of the Underdark, and lay beneath the High Forest between the cities of Menzoberranzan and Ched Nasad.

Description
Araumycos was a huge life form, a single organism that covered almost all the parts of the Underdark beneath the High Forest, beginning at a depth of 1 mile (1.6 kilometers) under the surface and ending at a depth of 3 miles (4.8 kilometers). It was believed to extend from the Shining Falls to the Lost Peaks and from Tall Trees to the Hall of Four Ghosts, wholly occupying the labyrinth of tunnels and caverns that existed beneath the High Forest. But it seemed that it had reached its peak of volume since it no longer grew through other territories by 1372 DR.

It was described as spongy, grey, and humid, similar to the outside of a brain.

History
The area where Araumycos was located was once mined and occupied by the dwarves of Ammarindar, during the time of the elf realm Eaerlann.

The dwarves of ancient Ammarindar told of how their mines located in the region beneath the elven realm of Eaerlann were abandoned to the slow, inexorable growth of Araumycos. The elves had legends that date back farther still, linking the birth of Araumycos to the fell sorceries of the Vyshaantar Empire, but so little was known of that era, even among the long memories of the elves, that no origin could be conclusively determined. Araumycos was thought by some to be the oldest living creature on Toril; even the gods did not speak of it, and divine divinations regarding the titanic fungus always failed. Some believed that the creature was an avatar of Psilofyr, the lord of the myconid, but this was only a theory.

After the Spellplague of 1385 DR, the rumored awareness of Araumycos was proven. Referring to itself as "King Araumycos", it brought millions of myconids under its domination, and tried to do the same with any sentient creature within hundreds of miles through strange nightmare-dreams (which the drow called golhyrrl' fhaazht or "the Dream Trap") that spoke of the comfort of the mass and the hopeless chaos of individuality.

Abilities
Araumycos was immune to magic and greatly resistant to psionic energy. Some areas of Araumycos could be attacked with normal weapons or were vulnerable to fire, acid, and other means, but destroyed parts grew back within a short time. Prior to the Spellplague, it seemed that the fungus was unaware of intruders and their destructive ways, but there were rumors telling otherwise. Araumycos had terrible defenses such as poisonous gas and enormous psionic power, and it could manifest slimy creatures similar to oozes. Araumycos could also use spores to dominate the will of victims and emit substances that could animate skeletal remains upon which they clung.

From time to time, without explanation, large sections of Araumycos withered and decayed, revealing ancient, undisturbed caverns. These caverns sometimes contained ancient ruins and were greatly sought after (especially by the Shade Enclave). They were eventually reclaimed, either in hours or centuries.

Locations
Although Araumycos for the most part completely filled the tunnels it inhabited, a few areas were not entirely covered:
 * Blacktooth Rock: Blacktooth Rock was an intersection of tunnels in ruined Ammarindar named for a large black stalactite that looked like a fang biting into the fungus. The intersection was a layered chamber carved by the dwarves. It was passable but full of Araumycos.

Novels

 * Insurrection