The Super Mario Players
From the Super Mario Wiki
The Super Mario Players is the band that performs the theme song "Jump Up, Super Star!" in Super Mario Odyssey. The band can be seen during the game when Pauline sings the song with her four band members in the Metro Kingdom as well as in the starting area of the Darker Side of the Moon. Following the version 1.2.0 update released on February 21, 2018, Mario can purchase clothing based on the band members' costumes, the Musician Hat and Outfit, from the Crazy Cap shops after completing the main game.
In Super Smash Bros. Ultimate, the Super Mario Players appear in the background of New Donk City Hall if the songs "Jump Up, Super Star!" or "Ground Theme (Band Performance) - Super Mario Bros." are selected as the background music. At the start of the match, only the drummer is heard, who appears on the ground. As the players ascend, the rest of the band members (including Pauline if the former song is selected) appear on-screen on propeller platforms. Hitting one of the band members will have him play their instrument. The Super Mario Players are absent if any other song is selected.