An Otyugh stands on 4 large legs and has a body 8 feet in diameter, weighing about 500 pounds. Behind its large mouth are 3 tentacles. When so inclined, an otyugh can communicate verbally using the predominate language of the area, usually Common.

An otyugh attacks living creatures if it feels threatened or if it is hungry; otherwise it is content to remain hidden. An otyugh slashes and squeezes opponents with its tentacles, which it also uses to drag prey into its mouth. It deals automatic tentacle damage with a successful attack on every round that its prey is held. The bite of an otyugh is diseased, and the recipient of the attack must save vs. Poison or contract filth fever (incubation period 1d3 days; 1d3 reduction of both Dexterity and Constitution).

Otyughs are repulsive beasts that feed off the refuse and waste habitually discarded by other creatures. They are generally found in large rubbish pits and cisterns, being not always content with discards, they wait beneath the surface for anyone foolish enough to stray too close. Otyughs have no discernible head, the bulk of their form consisting of a great horn-plated torso supported by three stocky legs that conceal a powerful, sharp-toothed maw. Three long tentacular appendages extend from their bodies, two of which are hard and thorny, being used to attack and grapple prey; the third is actually a sensory organ with three eyes at its end, which are capable of 90-ft infravision. Lesser Otyughs are also capable of limited telepathy at a range of up to 30-ft, and Greater Otyughs up to 60 ft, but such communication is limited to simple thoughts and ideas.

Whilst Otyughs suffer no ill-effects from bright light, they do not like it, preferring to dwell in dark places that help them to strike with complete surprise, though their eyes, usually protruding above the surface, sometimes give them away. They can use their great tentacle like limbs to strike for 1d8 damage, or 1d12 in the case of the Greater Otyugh, but may also attempt to grapple their prey. Grappled opponents suffer 1d3+1 points of constriction damage per round and bite attacks against them are made with +2 to hit. A character with 18 strength can break free after one round of struggling, but other characters must make a successful Open Doors roll to do the same. Greater Otyughs may use grappled characters as shields; in doing so, they gain a +1 bonus to armour class and when attacked may make an attack roll of their own, which if successful results in the grappled character becoming the victim of the attack. Any character unfortunate enough to be bitten by an Otyugh is extremely likely to contract a disease, 1 in 5 cases of which are fatal.