Firefly is an animatronic made out of old Bonnie costume, made by Lindsay during the events of Five Nights At The Inventory. He appears to have one red LED eye in his yellow face, and his endoskeleton legs show along with his yellow arms and body.
Firefly was made by Lindsay when she got locked in the Inventory. He has control of the air ducts and pyrotechnics, thus he is able to burn cameras, including Watchman, and break vent doors. Firefly is introduced on Night 3. Later, when The Cutting Crew is reinstated, Firefly serves food, occasionally performs, and helps kill night guards.
General: Firefly is very humble and nice, but he gets angry when people attack the Cuttting Crew.
Bonnie- Firefly likes him a lot, as he got his costume from him. Bonnie doesn't really care for him, though.
Metal Freddy- He teases him a lot. Firefly always has his flamethrower ready for him, though.
Cutting Crew- He's like a intern; he's learning to be a part of the Crew so he can fight.
-Firefly's design comes the villain of the same name made by DC Comics. Originally, he looked a lot more like him. His design now looks more like Springtrap.
-Firefly's head is seen the final teaser of Five Nights At The Inventory, while Lindsay is talking about him.
-The idea was to at first make Firefly disable cameras by lighting them, but this made him just like Lindsay. Instead, his flames block camera's views and busting vent gates.
-Firefly went through several names; Blaze, Burn, Scorch, and finally Firefly.
-Firefly was originally going to be made out of a Chica costume, as revealed in the final teaser in Five Nights At The Inventory.
"Hello, friends! Need anything heated?"
"Fine job disabling cameras, Miss Lindsay!"
"To burn to death, or to not burn to death...to take arms against the seas of fire, or to stay humble at the feet of destruction? That is the question."(Credit to Aidan for the amazing quote,..:3)