Hallucinations are easter eggs in the Five Nights at Freddy's series. They happen randomly, and usually Freddy's face pops up on the screen, along with the text "IT'S ME" and then Bonnie's face with/without eyes. Sometimes, when you start the game, you will see hallucinations and then it will go back to the menu.
Purple/ Shadow Freddy
Upon viewing the camera and looking at the Parts/Service room you can see in Withered Bonnie position a slumped over position like Golden Freddy but instead is purple, upon looking at him too long your game will crash, but it is assumed this is only in mobile version.
On a rare occasion upon putting your monitor down a floating figure who is the shape of Toy Bonnie but is all shadowed out except for bright white eyes and teeth can be seen, viewing the figure too long before putting the monitor back up up will crash your game this is on PC or Mobile.
On rare occasion a Bare endoskeleton can be seen on map right next to the puppet box in Prize Corner he can also be seen in the Left Air Vent though he will block out any other actual animatronic trying to get into the vent so this makes this kind of useful yet unfair. This does disprove the fact that animatronics try to kill anyone out of costume and try to stuff them into one as no one tries to put this bare endoskeleton into a suit.
Paper Balloon Boy cut out
On another rare occasion a Balloon Boy paper plate will disappear onto the wall in Party Room 4 and than appear on almost the top of the wall kind of transparent in your office. Their is no reason why this is a thing as it does not at all affect game play or has an effect on anything else.
If you start the game their is a rare chance you will be greeted by an Eyeless Withered Foxy it is unknown why it is here as it does not affect gameplay or affects anything else. If you start a night you will be greeted by an eyeless Toy Bonnie, once again it is unknown why it is here as it does not affect gameplay or affects anything else. Upon losing the night you will be greeted by an eyeless Withered Freddy one more time it is unknown why it is here as it does not affect gameplay or affects anything else.