i heard the bible believed demons can appear as humans even as humans that actually exhist and pretend to be someone close
So basicaly you've never read the bible and the entirety of your knowledge of biblical christianity is based on hearsay?
like your grandmother might be at her home sleeping but you get a knock on your door at 2am and a woman is outside who appears to be your grandmother but its not the real her
like a duplicate
This is reality you are dealing with, not some B rate horror movie. There are no demons wondering around impersonating people in order to get someone or other to trust them. Where do you get your ideas about demons? Ministering Deliverance? Because you certainly did not get it from the christian bible.
but what i read from the bible is that something will be off
No, you did not read that in the bible. And just to make certain I checked three different translations before responding to this quote. I could not find a single passage that claimed anything similar to what you say you read. You are either grossly misinformed by accepting hearsay that you agree with to be fact, or you are willfully lying in an attempt to make your fanfic seem credible or true.
they cant perfectly replicate a person, physically or intellectuall
Then what would be the point of the masquerade? How would a demon gain trust if it's so easy to figure out that it's not the person it claims? Why wouldn't it just appear as an angel and gain the victim trust that way? And what is the purpose of impersonating someone in the first place? What does it stand to gain?
so the person might have a slightly different eye color, or large pupils, talk strange, act different..
And yet it would still be able to dupe a person by assuming the form of a loved one or close friend?
Whatever your answers my point still stands. You have never even bothered to crack open your holy book and find out what it has to say on the matter, you would rather just accept the hearsay that you want to believe. Your lying to everybody and worst of all you are lying to yourself.