I don't think I have a awnser, but I do know there are secerets, if you have beaten the custom night, try, interacting, with the Doughnut on the desk. (it might not be on the desk, been almost a year since I last played.)
I can't think of anything else other than the custom night menu, but you probably found the 2 secret codes in it and beat 4 20 mode, I can't remember anything else from the game, so I'm out of ideas...
