>>7142708
>An 'incarnated ET' is a demon
That is a bit of an over-simplifcation, anon. There are a few different categories of entities to consider.
EBE
Extra-dimensional biological entities, commonly described as Demons, are physical incarnations of (usually malevolent) spiritual or "ethereal" beings that have taken physical form in our reality. Unlike living things, which are connected to the universe via the life energy of their soul from higher realms "above" and "outside" of reality, demons tend to "burrow up" into our reality from deeper, darker places. When normal beings die, their soul detaches from their body and ascends, and the body remains to be reclaimed by nature. When a demon dies, the animating force responsible for incarnation of the body is completely gone, as it sinks back down into a lower plane of reality. The body can no longer sustain its shape, and will either violently combust into almost nothing, or will gradually decay into ashes, which then fade out of existence without fireworks. This depends on the relative power exerted by the being in forming its body.
ET
Extra-terrestrials. These are normal, living beings that have their origins on planets outside the Sol system. Some races of ETs are infested by demons and are thus hybrids of ET and EBE. Some races can be temporarily controlled by demonic races, effectively worn like a suit, and may or may not maintain awareness while thusly controlled.
AB
Astral beings. Beings existing in the astral plane (or sometimes, other higher planes) who do not have physical bodies in our reality. They typically interact with us through thoughts or dreams, both of which take place in these higher dimensions as well. Some more learned and powerful astral beings can manifest as lights, geometric shapes, or other dazzling phenomenon in our reality on a temporary or permanent basis. Angels fall into this category!
Terrans
Terrans are sentient beings native to Earth. Besides Humans, there is also a species of subterranean reptiles that evolved from a saurian species that survived the extinction of super-reptiles on the surface millions of years ago by adapting to life in caverns. There is also a sasquatch-like hominid race that shares a very, very distant ancestor with humans (longer ago than the apes, even). They also live primarily in the underground, and they are aggressive and territorial–they do not make good neighbors. There is also a race of stocky, wide, and muscular human-like beings beneath the mountains in east Asia. If you saw them, you might call them Dwarves, although they are much taller and stronger than humans. The writers of the Norse Eddas knew of these beings.