Since the fall of Lucifer, the darkness within has been fed by those whose fall most symbolized it. First, the angels of heaven who rebelled and were cast into shadow. Then those lesser demons born of the dark prince and Adam's first bride. Finally, by their own as they were corrupted from within.
As the fallen and the infernal intermingled with humanity, they produced offspring. Something that ironically would have never happened were they not cast out in the first place.
These scions of Hell and Humanity were known by many names (imps, mares, fiends, etc.), but the most common was Succubi for females and Incubus for males. Those of neither gender refer to themselves simply as Imps.
They cannot feed off souls as a full demon can and instead sustain themselves with the life energy of humanity and other living creatures.
They resemble human beings but usually have some, or any, of the following: horns, hooves/claws, tails, or wings. Often all four, or any of the combinations. It's not as common, but some are born with none of these attributes, appearing completely human.
Because of their food source, Imps are intensely social creatures. They feel anxious without other living beings around. To them, loneliness feels similar to starvation in human beings.
They often live in loose groupings, instinctively seeking a community. Not in the same sense as Lycanthrope packs or Covens of Witches. They don't work in teams, but they rarely live alone, preferring more bohemian communal living spaces.
Quasi Immortal. Technically immortal, immune to the effects of illness and aging, Succubi/Incubi will live forever unless killed.
Like their Nephilim counterparts, Imps can possess many or any of the same abilities of their demonic parents, but to a far lesser extent.
Soul Drain. Their more unique ability is a more human variation on their progenitor's ability to take possession of souls, where they can drain the life force of a human being.
Pheromones. They secrete pheromones that can have physically addictive effects and may cause mental instability. It transmits as a toxin and can be absorbed through casual touch and scent, typically giving the target/donor a harmless euphoric high. The taking might leave them mildly tired but rarely results in death.
This is a more complex process than it sounds. They can't simply just do it. There must be a connection of some sort, primarily a physical one, but emotional will work as well.
Empath. They can read others' emotions and thoughts, but only when feeding.
Succubi and Incubi are superhumanly strong, about on the same level as older vampires and alpha werewolves.
They are naturally charismatic. Like angler fish, they lure in their prey. Their features, body language, natural air, etc., something indescribable about them lures others in and makes them want to get closer. This is somewhat involuntary and can affect others even when they don't mean it to.
Due to necessity in how they must feed, they are incredibly good at reading and seducing people.
They often face stigma for being born bad, no matter where they actually stand morally.
They can eat typical human food and drink but are only sustained by the life force of others. They can do this without any permanent harm to their targets, but once they begin feeding, it can be hard for them to control themselves. The more they drink, the lower their inhibitions.
They often feed energetically rather than through fluid transmissions because close contact can cause their target to become enthralled.
Their blood can be particularly appealing to vampires if they have recently fed. Vampires consider them nearly irresistible prey.