One of FNAF2's odd animatronics.
About Balloon Boy: Balloon Boy resides in the game area, holding a balloon along with a sign. Some people believe Balloon Boy to be a hallucination, while others think he doesn't really exist. These two theories are mainly derived from the fact that Balloon Boy contains no endoskeleton, as shown by the security cameras when he is present in the left vent.
Of course, in the actual game BB (Balloon Boy) does not have tear marks running down his eyes. I added the tears because the security guards neglect BB when he's only trying to say "hello." Also, the sign actually says "Balloons!", rather than asking hello.