Spoilers ahead.
After night 5, 'The party' the Protagonist is taken by kids wearing the Masks of the animatronics towards Fredbear/Golden Freddy.
They then say 'He wants to give Fredbear a 'Kiss'. So, that stuff his head into the Jaw of Fredbear and... Chomp.
Things that have been discovered thanks to this game;
Who is Fredbear
Who caused the Bite of '87. [or maybe the First kid's death. I think it's the bite though.]
The Victim of the Bite of '87.
Good god Scott. You did give us answers, finally.