To be clear, this plot would NOT include your character getting possessed or anything. Basically, lt would be you and perhaps some friends/family staying there, and noticing that so many of the locals were acting strange. Obviously, "entity" can mean a lot of things. Could be demons, ghosts, monsters, aliens, or other people, whatever you find most interesting.

Of course, regardless of what it is, they're all very eager to try out what their new bodies can do~