Doom Dancer Music Box
From the Super Mario Wiki, the Mario encyclopedia
The Doom Dancer gets its name from its ability to force anyone to dance at any speed whenever its owner cranks it. Mario, Luigi, Princess Toadstool, and Toad were after the Music Box in order to put a stop to King Koopa and his Koopalings.
Eventually, word got out to the Koopas, and Cheatsy, Big Mouth, and Bully were sent out to retrieve it. Bully's initial plan was to mutinously take control of his father with the device and become king over Dark Land, but King Koopa's cold stopped him from doing so (and also forced him to comply with the original plan, giving the Doom Dancer to his father).
When King Koopa acquired the Doom Dancer, he forced the entire Mushroom Kingdom to dance to his song Do the Koopa, a song that shared its name with the episode title. Mario, plugging his ears with Plumber's Putty, managed to dance his way over to Koopa and fight for the Music Box; however, it broke to bits when it fell off the Doomship onto a Goomba. The Doom Dancer Music Box may have been inspired by the Music Box items from Super Mario Bros. 3.