The original non-human beings: Archetypes. The most powerful beings on the Astral planes. What are they? Where did they come from? What can they do?
Well, strange though it may sound, they were created by humans, just like the Astral planes themselves. This may seem strange, since I've said they're much more powerful than humans, so I'll explain:
When you're in the Astral plane, you're in a land of thought made real. Since thought energy is substance here, it is obvious that you can create things here, just by concentrating on them; your Astral energy will leave your body and become the object you wish to create. Now, this object can be just that, an inanimate object, or it can have a LIMITED degree of sentience, and I do mean limited. You can only create what you can understand, and consciousness is a very difficult concept.
However, just because you alone can't do something doesn't mean it can't be done. Two people concentrating can make an object that is larger, or more powerful, but they can also make it more sentient. Three people can make it even more so, and so on...
This doesn't mean that you could get together with a group of friends and create a living, sentient being on the Astral plane; it takes THOUSANDS of people to create an independant being, if not millions. So, you cannot CREATE an Archetype deliberately.
Rather, they come from the 'collective consciousness' of mankind. In the case of the creaures normally found in horror stories, from fear. Consider early man, sitting in his cave at night. Every shadow a threat, every noise a predator. And everything, in his mind, becomes 'larger than life'; a wolf becomes a werewolf. A bat becomes a vampire. A lizard becomes a dragon. The wind becomes a ghost. And so on. Many predators become anthropomorphised, taking on human characteristics (werewolf) or even BECOME a human with slightly animal characteristics (vampire).
This fear was collective; EVERY human felt the same. And it has stayed with us ever since, in stories and myths. Every culture in the world has a version of the vampire. So, at one time, ALL humans in the world were afraid of supernatural beings. And fear is a strong emotion. And all that fear collected up in the Astral planes lead to the creation of Archetypes. As stories were made up and told of the various monsters of the night, the Archetypes became stronger and better-defined, and more numerous. Until there was an Archetype of vampires, an Archetype of werewolves, and so on.
But, once they were created, by their nature, they wanted to grow more powerful. So, they needed more people to fear them, to BELIEVE in them. That, you see, is the key to supernatural beings; belief makes them stronger. When you believe in something, you think about them. Every time you think about a vampire, that thought goes to the vampire archetype, and makes it a little bit stronger.
At first they probably went abroad in the night, and encouraged belief in themselves. But, that would have taken effort, and using energy to earn it meant a smaller return. So, a method of spreading fear and belief that DIDN'T require any energy or effort? Obvious: give humans certain abilities like their own. Then, people will come across these supernatural/human hybrids, with the appearance and powers of the real Archetype. This will make them believe in the Archetype, and so will give the Archetypes power, at absolutely no cost to them.
Also, by making it possible for these human avatars to create more of their own kind, it meant that only ONE avatar needed to be created, and many more could be created, again with no cost to the Archetype.
So, that's how Archetypes came into existance, and how they came to make humans with similar (tho reduced) power to themselves. It's also how Gods, Devils, Demons and Angels came into existance. In fact, how ALL supernaturals came into existance. For that matter, fantasy creatures such as dragons, unicorns, elves and the like are also present on the Astral Planes, since they are also believed in and thought about. You could meet them, if you were willing to search for them. Of course, to do that, you would have to gain access to the Astral planes.