Endo-Unknown

Endo-Unknown is one of the only characters who doesn't directly harm the player, and is mostly off-screen.

Background
He is a failed endoskeleton, likely due to the jaw and eyes, as the eyes were uneven, and the jaw didn't hold in most of the teeth, nor did both sides stay connected. This Endoskeleton has programming that makes it act like a shy, but kind person. They like covering your eyes and randomly jumping out to surprise the player, like a surprise birthday party.

Role In Story
No true clear role, but likely will be explained in the future.

FredBear's Ultimate Custom Night
Endo-Unknown just appears behind the player, on the left or right, but causes no harm.

Endo-Skeleton Ultimate Custom Night
They are behind a pile of crates. They slowly start to peek out from the pile. The player must shine their flashlight in the face of Endo-Unknown to make her go back behind the crates.

Trivia

 * This is the first character to have a hanging jaw, the other being Phantom Endo-Springbonnie
 * The only difference is their jaw hinges are swapped, so Endo-Unknown's left part is hanging, while Endo-Springbonnie has his right side hanging