Outsiders

Demons
Outer-dimensional beings beyond classification, hailing from a world beyond our understanding. Their true forms are comprised of “matter” in the most literal sense of the words, and generally look abstract, surreal or even horrifying, but when crossing into U’rth they adopt forms that stick to the common sense of this reality and that they can shape on a whim. Nevertheless, their bodily properties and abilities still don’t quite fit, with varying details such as being mildly radioactive, weighting far more than they visually should, messing with electronics with their mere presence, melting reflective surfaces they stare at, or appearing as blurry clouds in photographs.

Demons can’t be killed by conventional means, for destroying their physical bodies in U’rth only sends their original selves back into their home dimension, to regain their strength. Powerful spells are required to truly obliterate a demon in both sense.

Demons don’t actually live in U’rth, but they sometimes cross over through a "rupture" in reality, located in the interior of what appears to be the ruins of a tremendous engine or structure