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.
In Super Smash Bros. Ultimate, the Super Mario Players appear in the background of New Donk City Hall, along with Pauline. Hitting one of the band members or Pauline herself will have them play a song.