The Phantom is a mysterious male spirit.
In 1996, this mysterious Grim Reaper-like ghost joined the Happy Haunts crew in the Haunted Mansion for Halloween, groaning and snarling as he ran up and down the Corridor of Doors with his scythe. He also attended the Mansion's 30th opening anniversary, standing in the alcove at the graveyard's exist to scare the guests one last time.
Behind the scenes
A live character played by a costumed actor, the Phantom was added to the Haunted Mansion attraction in Disneyland in 1996 for the Mickey's Halloween Treat park-wide overlay. Despite the name, the character (who replace Lord Ravenscroft, a vampire played by the same actor in the previous edition of the event) bore no relation to the Phantom of Phantom Manor.
The Phantom was seen one last time in 1999 for the 30th anniversary of the Haunted Mansion, alongside the Knight of the Living Dead and several other live characters (like the Attic Phantom and the Ghostly Bridesmaids). There exists film footage of that appearance, and that appearance alone. Opinian didn't play him on this occasion.
The characters did not usually speak. However, in an interview, the actor recounted the one occasion where he did; a friend of his (playing a werewolf in another Land) asked Christiansen when his break was due. Unfortunately, a young girl had observed this. Unwilling to break character while observed, he instead answered “NIIIINE” in a sepulchral voice.