First subcluster -- "Otherkin"
The most basic "accepted" definition of Otherkin is that they are people who believe that they are essentially and significantly something other or more than human. I think that that is a fair definition of it, whether it comes via genetics or by soul-incarnation.
The definition that I do NOT agree with, though some insist on it in their own writings and subcultural lore, is that it is the incarnation of a "non-human" soul into a human body and nothing else. I.e., Angelic soul, Dragon soul, Starseed soul......which, to put it bluntly, is pure bullshit. Souls are souls, and they accumulate identity from every form that that they incarnate into. That's the way it works. And that's also why not every person who claims to be of multiple species/forms is blowing smoke....go around the block enough times with enough meaning, and you may wind up with a lot of interesting details on your curriculum vitae, whether they're part of the human train of development or not.
The people who go on about those puristic definitions either haven't been around long enough to have more experience, or they've chosen to remain within one non-human species only and built up a history there -- or, just possibly, they're in a bit of denial 'cause they're so attached to the idea of their essential self not being human. And therefore of having a superior and/or disinvolved relationship with the species whose basic form they just happen to have been born into. Or having a mission that will enable them to always maintain an elder and more-enlightened stance, rather than accepting that they too may have things to learn by virtue of their humanity.
Generally-Accepted Subspecies of Otherkin:
Vampires/Energy feeders: Psi (psychic energy), sang (blood), empathic, pranic, elemental. More on this later.
Therians -- "Werecreatures", or having tangible animal identity that either overlays or intersperses with the human awareness -- term implicitly includes mammals, fish, birds, reptiles & amphibians, both modern and prehistoric, even though "therian" technically denotes mammalian furry-type beasts. Insects are rare as claimed types, as are particularly small animals. More on this later.
Fae: Elves, Sidhe ('Seelie' & 'Unseelie'), Trolls, Dryads, Faeries, Changelings, etc......some of whom claim to have come originally not from other planets or galaxies but other dimensions (I think I'll invite litharriel to give a better overview of this).
Angelic/Celestial: Re/Incarnated Angels and superhuman intermediary/guiding powers in all their cultural/religious variations, Gods, Fallen Angels, Angels w/in hosts, Demons, Nephilim. Much more on this to come.
Starseed -- Extraterrestrial species incarnated as humans....there is some overlap with categories of Elves such as the Elenari, who also claim to have come from the stars.
Dragons -- Basically what I said, and there's too much of lore and fantasy and cultural mythology for me to address this one myself. Anyone who is a Dragon, feel free to fill in the generalities.
The jury is still out for me on Unicorns, btw. I don't have any proof that the Unicorn of Western symbolism is a "real creature" as opposed to a synthesized collection of ideal traits, so I tend to take that with a very large grain of salt. If you're a Kirin, though, step right up and present your case....
And then there are "non-human" non-biological identities that have no established social grouping so far, such as memories of being a star -- which I believe is quite plausible, though I've seen it challenged. This being a personal area of definition, I think it unwise to admit or deny anyone's self-validity based on general principles -- one must take into account the nature and awareness of the person who is making the claim and putting themselves forward.
[The next general area I'll address is that of states of consciousness and self-inhabitance, though some of the terms/types there are commonly assumed to be Otherkin per se rather than their own phenomena, such as walk-ins, multiples and 'Otakukin'/"fictionkin"....]