Manes

(from Dungeons & Dragons Monster Manual - 2014)

Souls of evil creatures that descend to the Lower Planes are transformed into manes — the lowest form of demonkind. These wretched fiends attack any non-demon they see, and they are called to the Material Plane by those seeking to sow death and chaos.

Orcus, the Prince of Undeath, has the power to transform manes into undead monsters, most often ghouls and shadows. Other demon lords feed on manes, destroying them utterly. Otherwise, killing a manes causes it to dissipate into a cloud of reeking vapor that reforms into another manes after one day.

(from Planescape Monstrous Compendium Appendix I - 1994)

Manes are the most pathetic beings on the lower layers of the Abyss, vast and endless as the layers themselves. [They] cannot communicate.

Manes travel in gibbering, snarling hordes that sometimes number in the thousands. Physically weak, they attack in such great numbers that non-tanar’ri fear them.

These wretched armies are difficult to maintain, for the manes are literally too stupid to understand commands. They can temporarily form a regiment, but they eventually wander about aimlessly, paying no heed to orders. If brought to a battle, however, they make excellent soldiers; once they see the enemy, they attack tirelessly. Sometimes they attack even when such a tactic does not favor their army, but such is war in the Abyss.

In the Abyss, manes are viewed as sub-tanar’ric and scorned by everything there. This does not bother the witless manes.

Like the dretches, the manes represent a major fighting force that is highly expendable. Unaware of their position in the Blood War, the manes have no way to improve the cruel treatment they receive.

When chaotic evil mortals from the Prime Material Plane die, their spirits go to the Abyss and become manes. Those who were particularly cruel and evil in life are confined to the Pits of Despair on the 400th layer of the Abyss. Of this place, wizards and sages know only the name, because none have ever seen it. The Pits are thought to be hidden beneath the Mountain of Woe, but again, little is known.

The lowly manes, plentiful and weak, have the dubious honor of serving as the primary food source in the Abyss. When a manes is eaten, it is destroyed utterly and will not reform.

Combat: Manes are nearly mindless, senseless creatures. They are immune to mind-affecting spells. They wander the Abyss in endless hordes, attacking all non-tanar’ri they encounter with two raking claws (1d2 damage each) and bite (1d4 damage).

When formed into legions, manes carry maces (1d8 damage). One major problem with arming the manes, however, is that they quickly forget how to use the maces, drop them, and fight with claws and teeth.

These creatures disregard their own existence. They never check morale and fight until slain. Killing a manes simply dissipates it into a noxious, stinking vapor that reforms in 24 hours. Anyone within 10’ of a manes when it dies must save vs. poison or sustain 1d6 damage from the acidic vapor.