Who resides inside the haunted manor that has the theme song "Grim Grinning Ghosts"?
Grim Grinning Ghosts: "Grim Grinning Ghosts (The Screaming Song)" is the theme song for the Haunted Mansion attractions at Disney theme parks. Haunted Mansion:  The attraction, although differing slightly in every location, places riders inside a haunted manor resided by "999 happy haunts".
"999 happy haunts"