Demon

Although sages group demons into types according to their power, the Abyss knows no such categories. Demons are spawned from the stuff of the Abyss in a near-infinite variety of shapes and abilities. The common forms that are familiar to demonologists represent broad trends, but individual demons defy those tendencies. For instance, a vrock might crawl out of an oil slick in the Demonweb Pits with three eyes and vestigial wings. A chasme might appear on the layer of Azzagrat possessing the ability to belch forth clouds of flies.
If a demon survives for centuries, it accumulates changes to its form due to interaction with the energies of the Abyss. These long-lived demons often become demon lords, beings of such power that they can hold sway over entire realms within the Abyss. A few demon lords have come to the attention of mortals and are even worshiped as gods in some places, but the vast majority of demon lords remain unknown to scholars and sages.