What do you consider a polymorph? Are all shapeshifters polymorphs? Do you consider polymorph to be a subtype of demon? If so, please explain why. Do you have memories of being incorporeal? If so, please describe your memories.
I don't consider all kinds of shapeshifters to be polymorphs.
I consider a "polymorph" to be a kind of non-physical entity, much like a demon or shadow, that's prime ability is being able to change it's shape, appearance, and even "feel" at will. It's a very loose definition, and rightly so, because in general terms what's commonly called a "polymorph" in the otherkin community is any shapeshifting spirit of unknown origins.
As for whether or not I consider a polymorph a kind of demon, I think that some are, yet others aren't. Like I said, it's a group loosely shoved together because of a few characteristics, for the sake of having something to call such entities. So obviously, some polymorphs are more demon-ish than others, and are more likely to fall under the "demon" label. The prime reason I myself don't use the term demon is only because there is the slightest energetic difference between what I would call a true demon and myself. I can't really describe in words what that difference is, but I think Meirya said it best when she called me something between a demon and a fae.
As for memories, I don't currently have any "hardcore" memories, but I do have memories in the sense of feelings and energetic sensations I may have experienced. For instance, I can faintly recall the feeling of weightlessness, and of moving just through my own will without physical muscle contraction and such. I can also remember the feeling of not having to breathe, and of not having a real "body". It's hard to describe the latter, it's sort of like.....I had a form, but it all felt like it was in perpetual motion while still being "me". Which brings up another subtle memory, the sense of "vibration". Those are the kinds of things I have memories of. So far, though, I can't remember anything I specifically did.