What was in the box?

Overview

For two years, one mystery has continued to linger over the FNAF franchise -- what was in the box? In FNAF 4, the final image is a locked box with the message "Some things are best left forgotten for now." But with the series over, now is the time to answer...WHAT WAS IN IT? Well, it's not all that easy to answer. Because it's my theory, my FNAF theory, that the contents of the box have changed three times. So what was meant to be in FNAF 4's box vs what ended up in it when the credits rolled in FNAF 6? I think we've already seen the solution!