Nightmare is a nightmare animatronic who first debuts in Five Nights at Freddy's 4 as the game's final antagonist. He is a recolored version of Nightmare Fredbear.
Nightmare's appearance is almost identical to Nightmare Fredbear's appearance; the only drastic differences are that the costume color is changed to black, and the bow-tie and top hat are changed from purple to yellow.
If images featuring Nightmare were brightened, it would reveal that Nightmare's costume is actually translucent, as if his endoskeleton is cloaked in a shadow. As such, nearly all of his endoskeleton can be seen by brightening images of him. The only exception is around his mouth, which appears to have an existing material ripped away from it.
Nightmare is a cruel, twisted animatronic who takes pleasure in tormenting his victims. This is apparent in Ultimate Custom Night, where he informs the player of their death in a rather sadistic manner. He also appears to enjoy mocking his victims upon getting the chance to do so. He also speaks using a deep, monstrous, intimidating voice, befitting his name.