This image is Nightmare on the Jump Scare, layered on top of Nightmare's jump scare. Not only is it creepy, it could symbolize something bigger. They are both in the exact same position. Even look at the mouth. Nightmare's teeth fit perfectly in Nightmare on the Gaping mouth. Not only that, but they have the same jump scare sound. Nightmare on was the replacement for Nightmare and the Halloween DLC, and in security breach, the Nightmare on Plush is called the Nightmare Plush. To me, I think this means that they both represent Death. Death comes in many forms. The reason Nightmare on isn't canon for na 4 is because in the story, Death takes the shadow form of Fredbear as it's related to how the crying child was killed. Maybe the reason Nightmare is the icon for Ultimate Custom Night is that it's actually him that is the vengeful spirit. Probably not, but it's still cool to think about.