Here is my (Walk) Playthrough for the nightmare boss level. First of all, the Location of the Boss Level is after you passing the electric door (unmissable). Go left Side two times and you see a Hole, fall down and at the next Wall left side is a very small gap, use it and here you will find the Bed aka Nightmare Boss Level. The level itself its one Room with the Boss, nothing more. On easy or Normal the Boss is no problem (you dont have play the Nightmare level on hard or Uber)