The Duathi are a twisted and corrupted faelen human sub species (though they can be mixed with Orrish and/or Faerie lineages). Their DNA and forms have been affected by the Void and/or The Deeping through prolonged exposure or Lovigdral experimentation.
They often do not consciously feel or process the pain of their twistings and corrupted form, though its internalization drives them to the brink of madness over time. They cannot generally physically stand up to a strong human of the same age – their greatest advantage is their numbers, which grow swiftly due to a slightly shorter gestation period.
Society: Do to their horrific sight and nature, they often hide from the other races in caves, tunnels, deep forests, and remote dark places, organizing into family bands that hunt outsiders to breed with to prevent inbreeding. Duathi have both a “high” and a “low” expression. High are higher functioning, intelligent and organized. The lower expressions are devolved completely. Usually horrific abominations and the senses, more like animals than humans. The higher order Duathi often use them as guards and pets.
Communication: They will settle on a language spoken by the eldest in the world and culture they came from, teaching that to successive generations. Additional, wheezes, whines, pops, clicks, and gestures will become added to a local vocabulary to allow simple ideas to be passed in a echo filled or vertigo impaired environment like The Deeping. It also allows better communication between High and Low order Duathi.
The Nurth of the Steel Realms are an example for a group of people that mate this terrible fate.