So out of my 17 ideas I’m going with this:

“Survival game where you are stuck in a room with a murderer or monster and you have to move from hiding place to hiding place without getting spotted. You can guess the movements of the murderer by what he says or does when hunting you and during a brief introduction into his murdering methods.”

I have the clearest image in my head as to how I want it to look and feel, and I can think up the most amount of interesting mechanics for it.

Now to design this game up!