The illithids, also known as Mind Flayers, are a race of lawful evil amphibious hermaphrodites with powerful psionic abilities. They are greatly feared throughout the Underdark. Adult mind flayers stand about six feet tall, are vaguely humanoid, and have hideous mauve skin that glistens with slime. Their heads have pupilless white eyes and four tentacles encircling a round, many-toothed orifice resembling that of a lamprey. Each hand has three reddish fingers and a thumb. Mind flayers employ a wide range of psionic powers, including their widely feared mind blasts. In addition, their tentacles are adapted for latching onto a victim’s skull and then burrowing into the brain.

Ixzan

The ixzan, also known as Demonrays and Spawn of Ilxendren, are closely related to their saltwater kin, the ixitxachitl, who dwell in the warm shallows of the surfaces’ seas. Ixzan are intelligent, typically chaotic evil creatures who resemble manta rays with barbed tails. Their colour varies: most have grey underbellies and mottled brown to grey upper surfaces. Ixzan are semi-amphibious and can survive out of water for one full turn before needing to return underwater to breathe. Ixzan attack with a powerful bite, although some mutants have an additional attack with their barbed tails. Several exceptional ixzan exist, including priest ixzan, wizard ixzan, mutant ixzan, and vamperic ixzan.

Kobolds

Kobolds are short, lawful evil humanoids with scaly hides that range from dark, rusty brown to rusty black, and a non prehensile, rat-like tails. Although kobolds are little more than pests in the Realms Above, competing with gnomes for food and living space, in the Underdark they are a major threat. Kobolds can quickly strip a region of resources if their numbers remain unchecked. The more powerful races of the Underdark enslave many kobolds; they are used primarily as front-line troops in the initial skirmishes of war.

Urds, relatives of kobolds with leathery bat-like wings, are largely unknown in the Underdark. A few tribes were once found dwelling in great chasms beneath the earth, but most have fallen victim to more powerful competitors such as cloakers and beholders.

Kua-toa

The kua-toa, also known derisively as Gogglers, are an ancient race of intelligent, typically neutral evil or chaotic evil fish men. They look like paunchy humans covered in scales, topped with a fish head. They have huge fish eyes, undersized arms and legs, and long, partially webbed hand and feet, with three fingers and an opposing digit. Kua-toa are typically pale gray in coloration; males have undertones of tan or yellow. Gogglers reek of dead fish. Their skin tone darkens when they are angry and pales when they are badly frightened. Adult kua-toa are amphibious.

Mongrelmen

Mongrelmen are grotesque, lawful neutral humanoids between five and seven feet tall. No two looks alike, since all mongrelmen descend from wildly mixed racial stock, including bugbear, bullywug, dwarf, elf, gnoll, hobgoblin, human, ogre, and orc blood, amongst others. They are ashamed of their appearances, and usually try to conceal their bodies from strangers.

Excelling at theft and camouflage, mongrelmen congregate in ruins or small shantytowns. In the Underdark, they live near the surface, where they can more easily scavenge or steal materials for their communities. These underground settlements usually connect to the surface in numerous places, providing easy escape. However, the Underdark is so filled with dangers that despite the creatures’ best efforts, mongrelmen settlements are usually short-lived affairs, attacked by hungry monsters or slave traders before they have much time to establish themselves.

Myconid

Orcs

Orcs are lawful evil humanoids with grey or green skin, coarse hair, a slightly stooped posture, a low, jutting forehead, canine teeth, and a snout instead of a nose. Despite their prevalence across Faerun, particularly in the abandoned dwarf holds of the north, orcs are far less common in the Underdark than one might expect. However, neutral evil orc-quaggoth crossbreeds, known as boogins, are growing in number throughout the upper reaches of the far northern Underdark as well as beneath the great forest of Cormanthyr.

Since the destruction of Hellgate Keep, a new breed of chaotic evil tiefling-orcs known as tanarukka have been growing in number in the upper reaches of the Underdark west of the Buried Realms beneath Anauroch in the tunnels once claimed by the dwarves of Ammarindar.

Pech

Pech, also known as rock children, are a race of small, neutral good humanoids from the elemental plane of earth. They sometimes make their way into the deeper reaches of the lower Underdark to mine rich veins of ore and work the surrounding stone. They are very thin, with long arms and legs and broad hands and feet. Their flesh is nearly as hard as granite, coloured pale and yellowish with red or reddish brown hair. Their eyes are large and have no pupils. Pech often compete with dao, the various dwarven races, and thaalud for raw materials, but these elemental earthkin are otherwise left alone by the other races they encounter.

Phaerimm

Phaerimm are a race of powerful sorcerers whose mastery of the Art is sufficient to rival that of the Chosen of Mystra. They resemble upright cones, their widest part uppermost, and the point ending in a barbed stinger tail. Phaerimm were largely responsible for the fall of Netheril and the spread of Anauroch to cover once-fertile land. The efforts of the sharn confined the phaerimm beneath Anauroch, although a few individuals are believed to have escaped the magical prison confining the rest of the race or perhaps were caught outside the barrier when it was erected. Rumours of phaerimm activity involve both the Twisted Rune and tune ruins of Myth Drannor.