What are demons?

Are demons fallen angels or are they a separate species?

Are they physical beings or spirits? or both?

Are there good demons and bad demons or all they all evil?

Where do they come from?

Who are you asking?

Because you'd probably get a different answer from each religion, country or continent. If we assume they exist to begin with, there is no obvious 110% confirmed fact.

I can say one thing though: by the very definition of the word, there are no "good" or "bad" demons. They're simply demons and they would define their own path outside our preconceptions.

I think all of the above.
Ive been attacked by what I thought were physical demons, I felt them tearing at my legs and trying to devour me, at which point I had an epiphany that nothing was really physical, and at which point the demons and the rest of physical reality disappeared. I had marks on my legs when I returned from the void.
I now know they can be real if you let them be. It has a lot to do with intension and expectation of your reality.

I say do an experiment, get out the ouiji, call out some demons, and when they get there, laugh at their presence, I say laugh because if you end up being scared, they will probably attack you until you realize the power you have over them.

My understanding is that a Demon can be any earthbound spirit that has never lived in human form. Most folks associate demons with evil however I believe that is not true. Like all things in nature they are duo both positive and negative depending on circumstances. Check out the Goetia is a good starting point for demonology.

Peace
Trustnobody