The Hatbox Ghost is a legendary figure in Disneyland history. The original Audio-Animatronic was in the Haunted Mansion when the attraction opened, but was removed a very short while later because the effect (hat goes from head into the hatbox) didn't work.
For more about the Hatbox Ghost and the history of the Disneyland Haunted Mansion, check out our full history of the Haunted Mansion.
A couple of months ago a wall appeared outside of the attic scene before the graveyard inside of the mansion. It is assumed that this will be the spot that the Hatbox Ghost will return to.