JJ (Fnaf 2)
JJ looks mostly like a female Balloon Boy, with more pink and purple accessories, whereas Balloon Boy has red and yellow.
Like Balloon Boy, JJ cannot be seen in the cameras, and will appear in the side vent at random. Close the door and wait for a thudding noise to send her packing.
In The Side Vent:
If you fail to close the vent quickly enough, JJ will go under your desk, and makes a laughing noise when she enters the office. While there the door controls will be completely disabled, which is why you need to pay close attention to the side vent when there’s a lot of animatronics to deal with.
In The Office: