Music Box
The Music Box is a common item found in Super Mario Bros. 3. It makes all Hammer Bros. on the map screen fall asleep so that Mario and Luigi can sneak past them. The song that's played is a soothing version of the Super Mario Bros. main theme song.
A Music Box (with a world inside of it) was actually the setting of Wario Land 3. In this game, Wario was sucked into the Music Box upon examining it, and met a mysterious figure inside one of its old temples. This figure stated that he was once the Music Box's ruler before a magic spell was placed upon him, leaving him trapped within the temple. The only thing that could undo the spell was five smaller Music Boxes, which Wario collected. In the end, it was revealed that this mysterious figure was actually the malicious Rudy the Clown, who challenged Wario to a fight. Wario ended up beating Rudy and freeing the Music Box's inhabitants, who let him leave their Music Box world.
