"Hey, Jake. It's Lisa, again! So, I want you to be careful on this night. There's this weird messed up Mickey in the Caverns with a floating head. It's... pretty messed up, let me tell you. But, I'm sure you'll be fine..." -LisaMyster Mouse is a multi-textured toon. He was created by FNAFXel1258, or known as Un Invert Mickey.
His appearance consists of sepia, photo-negative, grayscale, and normal Mickey colors. There are multiple tears on his suit, with his left shoe and glove missing. His head seems a bit distorted, and is floating. He also seems to have a lack of eyes. His body is also apparently dusty.
Myster Mouse starts in the Caverns Entrance, and slowly travels to the Meat Freezer, Lounge, then the Office. If he's directly in front of the desk, the player must shut off a camera. If he is at the far left door, the player must hide.
Occasionally, he will speak, but his words are reversed. His lines, if set to normal, are as follows:
"This will be your end."
"You can't run from the gates of hell."
"Your fucking body will be torn to shreds."
"Soon, your neck will be tightened around a hangman's noose."
His jumpscare consists of him popping up from below, grabbing his head, then throwing it directly at the player. If hiding, the player will be grabbed from under the desk by the headless body, then thrown at the wall.
- Strangely, Myster has a few similarities to Corruptus. It could be possible they are connected, but it is not explained how.
- When Myster is in the Caverns Entrance, his appearance is only as a withered Mickey. After he enters the Meat Freezer, however, his appearance changes. It is unknown why this is.
- One of Myster's quotes, "You can't run from the gates of hell," is a possible reference to how death is unavoidable, however, this has not been confirmed yet.
- Rarely, Myster will speak normally. It is unknown what the cause of this is.
- His first jumpscare screech originated from a screaming frog.
- Myster is also one of the antagonists in the Five Nights at Freddy's fan-game A Week at Castaway Cay.
- His behavior and jumpscare screech, however, are different.