User with this ability/Trait either is or can transform into a demon, an evil spirit or Satanic divinity. Most commonly user retains their general form but with some additions; horns, claws, fangs and tail are common, as are wings, more fit (muscular and/or larger) body and color change (red, blue or black dominate) but there are several kinds of demons who are far less humanoid, varying from strange, surreal or even absolutely horrific.
For practical reasons demons can be divided into three groups defined by what they are formed from:
- Physical Demons aren't necessarily solid matter, but they are material/energy beings with relatively defined/stable form and often at least somewhat human-like mind. Most users that aren't originally of demonic stock have this variation. Note that demons of this group aren't necessarily any weaker than those of the other groups, they are simply more "solid" in mind and body.
- Spiritual Demons are completely spiritual beings, and thus far less bound to the laws of physics or single form. Many of them think in ways that are only tangentially relatable to humans, and their forms are both transient and often downright surreal.
- Nether Demons are often both the most powerful and ancient demons, in some ways closer to sentient concepts than anything else. As such, relating to them in any way is likely impossible.
In most common senses, Demons are often portrayed to be weak or vulnerable to light, holy essence, or goodness.