Crying BB is a sprite of a Shadow Balloon Boy crying that appears in BB's Air Adventure from Five Nights at Freddy's 3.
Physical Appearance
He's a pitch black 8-bit representation of Balloon Boy, with gray tears striking down.
Mechanic
He will appear on the Glitch Floor, followed by his distorted laugh. While he's there, you will be unable to change cameras (you can still change systems and floors). Stare at him to make him leave. If he stays for too long, you'll die.