Okay, this is one of the wackiest theories I've come up with yet - so whacky that I'm not even sure if I believe it myself. I just want to know what others think.
We know that humans in the past have been infiltrated by fallen angels and maybe even the Nephilim. We also know that God himself wants to save as many as possible, so he will know who is children are.
Is there a chance that the ones who are cast into the lake of fire after the Tribulation are not really human, but are born to humans? They appear human on the outside and biologically have human bodies but are really the souls of demons. Is this why they do not repent, and why they take the mark, try to lead others astray and worship the Beast?