This article contains content (e.g: texture files, texts, etc.) that was not used in the series' final release. All of these files can be found in the game's files.
LivesIn the beta version, there was a life meter that would presumably limit the player's times of playing before they received the game over screen. However, this mechanic was not used in the final version of the game. Video footage of this feature can be found here.
Beta Monitor Map
The Monitor's early design shows different buttons for the camera. The camera icons were small circles with cones pointing in the direction they were facing. These cones may have indicated the camera's field of vision. They would turn green and become slightly larger when selected. Also some cameras were placed in slightly different locations.
The Backstage's camera was originally beside/behind the door, as indicated by the monitor pictures. The camera from the Kitchen was originally on the same wall as the door, pointing out directly into the center of the room.
Toy Chica in the OfficeThere is a texture of Toy Chica from the game files staring at the player with glossy-black eyes and lacking her beak and eye-lids. Her unused texture would have act similar to Toy Bonnie while using the Freddy Fazbear Head upon seeing her from the air vent. Interestingly enough, this texture is referred as "chicalookatyou" in the MFA files using Clickteam Fusion 2.5.
The Puppet in the Officethe Puppet's full body along with the marionette-like control and strings attached. According to the MFA files in Clickteam Fusion 2.5 program, this unused texture is named "puppet in office", suggesting that the Puppet was originally intended to appear in the Office in a similar fashion to Withered Freddy, Withered Bonnie, Withered Chica, and Toy Freddy.
Puppet's close-upAlso, there is an unused image of the Puppet's close-up resembling the last frame of its jumpscare, only closer and lacking white pupils.
Just like the first game, there is an unused Lives mechanic. There is a small bar that says "Lives" and a pixel stick-figure of a person with their arms outstretched.
Toxicity meterFreddy Fazbear Head equipped for too long. 
Found in the game files, there are a lot of leftovers of the Puppet's sprites from the second game, including its hallucination renders and the unused close-up image.
Within the games files, it is possible to find an unused button with the text "Seal Vent" on it. This button was likely going to be used to seal the vents, but in the final game it was replaced with double clicking the vent camera.
Found in the game files, there is a texture for the game's scrapped 7th night.
Like from the previous first and second game, there is an unused Lives mechanic. There is a small bar that says "Lives" and a pixel stick-figure of a person with their arms outstretched.
An unused "Chapter" text in pixelated font, supposedly used for the end-of-night minigames.
An animation file of a star. Its purpose is unknown.
Shocked BalloraBallora receiving a shock within the Primary Control Module location, with her endoskeleton face exposed.
Circus Baby imageAn unused small image of the red-tinted Circus Baby. It is literally unknown what purpose for this image is.
Molten Freddy's blueprintThere is a blueprint of Molten Freddy only found in the game files. It belongs supposedly to the rest of the blue prints found in the Insanity Ending. Despite being unused, the description for this blueprint is considered canon to the lore.
There are various buttons, likely intended for use with Cassette Man's tape recorder. Due to the tape recorder having actual buttons to interact, all four buttons went completely unused.
Horizontally-flipped Toy Chica
In the first release of the game, there was an obvious error showing both animations for Toy Chica (for entering the Office and jumpscaring the player) flipped horizontally. This was later fixed on update patch 1.021.
Horizontally-flipped Rockstar ChicaIn the game files, there is an unused file of Rockstar Chica with her position in the West Hall flipped horizontally, supposedly used for the East Hall. To avoid an error, a completely original position for Rockstar Chica in the East Hall was made.
Bonnet's animationsThere are complete leftover frames for the animation of Bonnet covering her nose from Sister Location found in the files. It was never necessarily used in-game, however.
Demo screenAn unused image found in the game files. This screen was supposed to be used for the game's actual demo before it actually ended up being a troll game. The demo screen mentions about starting a level when having over 2,000 points.