The below description is taken from LEGO.com.
“Boo! Did I scare ya?”
The spooky Specter really enjoys being a ghost. He delights in being able to fly right through walls, and gets a real kick (even if he doesn’t have any legs) out of lowering the temperature in a room just by hanging out there invisibly for a few minutes. His favorite pastime is to suddenly appear behind an unsuspecting Minifigure and loudly rattle his chain. The higher they jump, the better!
Yes, the Specter is a real prankster, but it’s all in the name of laughs for this fun-loving phantasm. And he doesn’t mind being pranked in turn, either. One time, the other monsters got together and called a team of ghost hunters from the big city to chase him around for a while. He’s still laughing about that one!