That question is so easy

I would make a game about being a killer it'd be like the new Saints Row in that style would be an opening cutscene the narrator would be a teenage boy he would be telling the story of your killer throughout the story you can choose if you hunt street a or a house or a day you could have killed your family or murderd trick or treaters on Halloween or you could have died in a school fire there's three classes

Class 1 serial killer your normal person who kills people if you place down traps you can blend in with people easier

Class 2 a being you died and come back to life attacks do nearly no damage you're big and you don't talk much it is harder for you to blend in with people

Class 3 nightmare you are a spiritual demon you can teleport people to a world of your creation you take less damage in your world but in the real world attacks do more damage you can work matter and reality to get your victim without a disguise you cannot blend in with crowd

After choosing a class you have to design your character throughout the game you can get more costumes

You can get perks called Killers runes from side quest

If you want to keep your reputation you have to kill a group of people every night your reputation goes down the less people you kill at night

There will be a bunch of Easter eggs classic horror murders

Depending on your backstory you have to kill the people who have wronged you whether that be your family your friend or a bully

You can choose your signature murder weapon and get skins for your weapons from side quest and stores

The entire game would be open world needing you to go to different graveyards for fast travel and to show areasareas of the map

And the game will of course be called KILLERS OF THE NIGHT