Nightmare is the True Main Antagonist of FNAF 4 and It's Series.He is the Child that is the Victim of 83.
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Trivia
He is Similair to Few Villains
Venom: Both Wear Black and Seek Revenge
Scar: Both are Younger Brother of the Hero, Both are Tragic,Both hate Their Brother,Both are Fallen Heroes,Both are Complete Monsters.
Chernabog: Both are Devils
Hades: Both are Immortals
Ego: Both are Fathers of the Protagonist and Both are Pure Evil.
He is one of the few FNAF Villains to be a comeplete monsters,others are Ballora and Tyrone.