possessed is a strong word in my experience people can only be slightly manipulated, it would take power of the scales for a demon to actually control someone or a weary manipulable person who does whatever he or she is told for a demon to actually have any power, or if the first person lets it sit in the drivers seat so to speek i suppose but under normal circumstances no
I think you are talking about the xtian theories right? If so, I think xian way to thing in this forum is not the correct place. What was your source, did you really studied something about demonic entities or spirits ? There is many differences and concepts, be sure from which side you are using as reference
I think that the real demons do not do possessed anyone.
By my opinion it is mostly a practice a lower spiritual beings, or black magicians. Maybe in some cases an product of your own mind too.
"A larva is something you create yourself, subconsciously, out of your own astra-mental energy."
Good protection could be your own meditation. And if an attack is very strong, so evocation of higher spiritual beings.
Its hard to tell if your the one being possessed they don't control you actions like making you walk off cliffs and such its like a voice in your head but the thing is its hard to tell the difference between your own thought and what the being possessing you is saying.
It's a complicated question. There are cases of one who's possessed being able to speak in other languages/do weird things. So in that case yes. But in others mental illness is mistaken for possession.
As a spiritual satanist I find what you ask quite offensive.Is clearly you don't know many things about demons.Study and you will find that they can be very friendly.They are not the ugly bad monsters.