You know, I don't know if you do too, but ever since the game came out, I've thought of the Nightamers as demons.

Which is symbolic because Fredbear was a factor in the death of the Crying Child (Evan i suppose), and black is strongly associated with mourning and death.

And well, apart from being death, it's not peaceful, since Crying Child is suffering in the coma, and being like the torment of all the physical and psychological agony he feels thanks to what he experienced in life with his brother, he is very aggressive, almost a demon that won't leave him in peace, since FNAF4 seems to be in a limbo, between life and death.

And well... I wanted to portray this, since I think Nightamer had a lot of potential to be a villain in the game and as a character in general.

(This is a headcanon thing, don't take this to seriously)