In the rideEdit
The Shadow Pianist appears in the Attic of the Mansion in the Disneyland ride, although not in the Tokyo Disneyland version, possibly because his character is related to Constance Hatchaway. He appears as a cloaked shadow wearing a top hat and a high collar, playing a dissonant, slowed-down version of Here comes the bride. The audio of the piano is heard in the Walt Disney World attic, though the piano and shadow are absent.
Being a cloaked, high-collar- and top-hat-wearing ghost haunting the Attic, the Shadow Pianist has been believed by many to be the long-awaited return of the Hatbox Ghost to the Haunted Mansion. Although this identification has been popping up much less often since May of 2015, now that the Hatbox Ghost, fully materialized instead of just a shadow, makes an appearance later in the ride. However, it should be noted that the Hatbox Ghost cannot be seen from where you see the Shadow Pianist and vice-versa, which means that like the Raven or the Prisoner, this could still be the same character, with in two different animatronics. On the other hand, the Hatbox Ghost's hat is taller than the Shadow Pianist's, and it has a straighter border.
Only in Walt Disney World and Tokyo Disneyland, there is a Music Room where the shadow of an invisible ghost pianist is projected on the wooden ground. This tableau, which predates the addition of the Shadow Pianist to Disneyland, likely served as inspiration for the character, who can be seen as an update of the Music Room effect. Some have taken it a step further and believe the Music Room pianist and the Attic shadow pianist to outright be the same character.
Interestingly, according to Imagineer Jason Surrell, the Music Room pianist is none other than the Ghost Host himself. If this is true, then the connection becomes impossible, as the Ghost Host clearly states before the guests enter the attic that he is going off partying for a little while and that they must now tour alone, only meeting again with them at the end of the Graveyard Jamboree ("Ah, there you are!"), which means he couldn't be in the attic at the same time.