He is clearly based on Nightmare Fredbear, being some sort of black, translucent, demonic version of the already demonic looking Fredbear. Unlike Fredbear, his skin is translucent, exposing all of his animatronic parts including the endoskeleton. Upon closer examination, a black mass resides in Nightmare's head, theorized to represent the Child's bitten off frontal lobe. But the same looking head appears as Mangle's second head so it is unknown what Nightmare's human-like head is.
Nightmare will only be seen in Nightmare Mode and 20/20/20/20 mode from 4 AM on. While Nightmare is active, no other animatronics will be active. He will show up at either hall and failing to close the door will either give a game over or him sneaking into your room. Once Nightmare is in your room, his head will be seen on the bed or in the closet. And when Nightmare catches you his jumpscare will be a still Picture of Nightmare while a garbled "scream" at the player.
The only cheats that have Nightmare involved are the "All Nightmare" and "House Map" cheats. The All Nightmare mode is, quite obvious. On the house map, Nightmare will show up as an Orange Square.
- He is similar to Shadow Freddy and Nightmare Fredbear in several ways.
- His current role in the story is unknown.
- Nightmare is the only one animatronic who doesn't have a jumpscare in the Extras Menu.
- Nightmare is the only animatronic in the fourth game who doesn't have an animated jumpscare similar to Golden Freddy from the first game.
- Upon close inspection, Nightmare has transparent parts in is body, this could imply that he is a ghost.
- An opinion gives that his black appearance makes him a spirit.