Nightmare Mousiki is an antagonist in Fredbear and Friends: Left to Rot.
Nightmare Mousiki is a large grey mouse animatronic. He bears a striking resemblance to the Nightmare animatronics from FNaF 4 in that his suit is dull, ripped, and he possesses several rows of large sharp teeth and pointed metal claws on the tips of his fingers. He wears a bowler hat, a red bowtie, and a brown waistcoat.
Nightmare Mousiki's only appearance during the main game is in Test Room 01 alongside Rodger. He can attack in two ways, the first being from behind either of the test room's doors. The player must pry the vent off the wall behind them open to escape, however Mousiki will attempt to attack during this period. He has a very quiet audio cue so the player needs to frequently check behind them to see if he is approaching. He will enter either of the two doors to the room, and the player needs to repel him by using space to 'Hyperflash' him with the flashlight. Failing to do this will result in a jumpscare.
Nightmare Mousiki is also one of the potentially active animatronics in Custom Room. His AI can be set from 1 - 20, or can be set to 0 to completely disable him. Mousiki will appear in the right hallway and is repelled by using space to 'Hyperflash' him with the flashlight. Failing to do this in time will result in a jumpscare. The number that his AI is set to will determine how frequently he appears in the hallway and how much time the player has to flash him before he attacks.
- Nightmare Mousiki's relation to Scrapped Mousiki from Fredbear's Fright is currently unknown.
- It is revealed during Custom Room that the name of the spirit possessing Nightmare Mousiki is Timothy.
- Nightmare Mousiki is the only character to share his extras menu image with another character, this being Rodger.