Nightmare (FNAF)

Just like Fredbear on Night 6, Night 7, and Night 8, he takes the same role, appearing at 4 AM, and replacing all animatronics, taking up their duties. He must be handled the same way, but Nightmare is more aggressive than Fredbear. Also, he always directly appears at the doorway. Upon being attacked by him, he will appear in a screen similar to Golden Freddy instead of a complete animation. His existence is unexplained, and his purpose is unknown. He is acknowledged in the gallery as a separate entity from Nightmare Fredbear, meaning that he must have some sort of significance. He is the True Main Antagonist of FNAF 4 and its Series.

Trivia
He is Similair to Few Villains

Venom: Both Wear Black and Seek Revenge

Hades: Both are Immortals

Scar:Both are evil Uncles, Tragic, and  pure evil

Ego: Both are Fathers of the Protagonist and Both are Pure Evil.

He looks similar to Shadow Freddy. Some fans theorize that they are the one and the same.

It's theorized that he is the Crying Child from FNAF 4 Minigames, because Nightmare doesn't appear until Night 6, after the child dies.

He is more challenging than the other nightmare animatronics.

His endoskeleton head seems to resemble a brain.

He is one of the FNAF Villains to be pure evil,others such as William Afton ,Tyrone,Ballora,and Twisted Freddy

His FNAF World counterpart is Honorable, this one is Pure Evil