Primary Control Module & Circus Control Sounds
Primary Control Module
When the player is in the Primary Control Module, clicking on certain objects creates strange sounds. Clicking on the Ennard mask's nose makes a crying noise, and other sounds are produced by the three baby heads and strange toy near Funtime Auditorium when clicked.
When the player is in the Circus Control, clicking on certain objects creates strange sounds, clicking on the dashboard makes a futuristic beeping noise.
There is an easter egg that can occur in the Elevator and in Circus Control, where BidyBab peeks through the window.
Eggs Benedict's Home
Rarely, when watching The Immortal and The Restless, in Eggs Benedict's Home, a Bidybab will appear watching the player from the bottom right, in the light.
Primary Control Module
There is a chance that a Minireena will appear spinning in the Primary Control Module on rare occasions. This may happen when you die to Ballora by a set number of times often.
Rarely when watching The Immortal and The Restless, in Eggs Benedict's Home, a Minireena will appear watching the player from the bottom left, in the dark.
Popcorn Easter Egg
Rarely during the Fake Ending, in Eggs Benedict's home, a Minireena can appear popping out of the popcorn bowl after eating some popcorn then immediately going down as seen here.
In the background of the game you can hear a slowed down version Baby saying the numbers "1578" in a random order it is unknown what this means in the lore currently. This most noticably plays in Circus Control, when offline, additionally Under the Desk.
FNaF 4 References
1983If you type 1-9-8-3 into the keypad while in the Private Room, it'll reveal 3 images from FNaF 4; The FNaF 4 Bed, Bedroom, and Plushtrap's hallway. This doesn't work during Custom Night's modes with Funtime Lolbit. However, due to this Easter Egg being a part of the Fake Ending and Custom Night it is Non-Canon. However Scott have clarity that this the actual date when FNaF 4 takes place.
Breaker Room Map
If you look closely on the Breaker Room map when restarting the power you can notice the FNaF 4 house layout, minigame layout, and Plushtrap's hallway layout.
Randomly when entering an area or booting the game a blueprint of one of the 4 main animatronics well show on the screen.
There is a incredibly small chance that Ennard's mask in the Primary Control Module will be replaced by Lolbit's head. This may happen when you die to Funtime Foxy by a set number of times often, similar to Minireena's Easter egg from the Primary Control Module.
The endoskeleton's appearance seems to look identical to Funtime Freddy's actual endoskeleton, though with few differences - A lack of "face-frames", wider eye spacing, having both hands (which would include the lack of Bon-Bon), and most noticeably yellow irises.
Like in every FNaF game your able to honk a Freddy's nose, in Sister Location you can honk the Fredbear plush's nose, this is only possible in Custom Night.