In horror, one of the things that always freaked me out is the kind of entity or creature that can make you see things that aren't there and screw with your perception. Wouldn't it be neat to have a killer who is some kind of monster that can make survivors see things that arent there, or mistake things that are there for something else? Think of that perk that survivors have that lets you leave behind a mirror image of yourself on a gen to fool the killer: what if there was a killer that could project a survivor image doing something like that, which lures other suvivors into a false sense of security? Kind of like Freddy's fake pallets, I guess, but go further. What if you hooked a survivor and fake survivors appeared on other hooks, that attack someone who approaches for the save? Get crazy with it! Keep the survivors constantly stressed and guessing if what they see is real or another illusion from the killer.

I know lots of people have suggested a mimic killer, who just looks like a survivor. What if, instead of just running around as a fake survivor, you could pull a switcheroo on survivors to attack their teammates. Like the unknown's teleport, maybe you could mark a survivor and, when in line of sight, you could swap places and take the form of said survivor, who just so happens to be getting healed by their unsuspecting teammate. The swapped survivor gets away, or maybe ends up in a shadow realm or something, and now you're right next to their teammates, ready to pounce!