This is a comments thread for the following album: https://downloads.khinsider.com/game-soundtracks/album/luigi-s-mansion-dark-moon
It plays when you're in the room with the Poltergeist in the Gloomy Manor. The music that plays on Boo levels and Paranormal Chaos are quasi-remixes of it (quasi because they're official).the Library Piano music sounds familiar idk why