These odd, half-skeletal creatures are summoned from raw, red manhole-like openings in the ground by Dark Cultists. They are quadrupedal, and look a bit like a dog crossed with a crocodile, then turned inside out. They are quick of foot, but appear to possess only melee attacks.
Dark Cultists do have an attack of their own, though whether they can summon creatures more fearsome than these guys is not known.
Media
See screenshots and concept art of the Dark Demon in the Image Gallery.