The Game Boy Horror is a device that Professor E. Gadd created in Luigi's Mansion. Luigi can use it to do many things. The Game Boy Horror has a map of the mansion, information about the Portrait Ghosts he has found, and a radar which helps him detect Boos. The player can also scan things, and Luigi will say something about them. If the player scans a mirror however, Luigi will be teleported to the mirror in the Foyer. The only mirror that can't do this is the one in the Mirror Room.
- It is quite obvious the the Game Boy Horror is modeled after the Game Boy Color. The word "horror" is colored like the word "color" on the Game Boy Color, and its design is just like the Game Boy Color's.
- If in a dark room, and the room is viewed through the Game Boy Horror, the player can hear ghosts singing the Luigi's Mansion theme.