That is Nintendo's Special Rock Band, playing at the Switch Experience in Tokyo. (Which was a day after the presentation.)
Nintendo's Special Rock Band along with their Special Big Band is basically Nintendo's in house band, basically their version of Sega's S.S.T (Sega Sound Team.)
Here's the big band.
EDIT: Added some more details to prevent confusion.
Wario had a move where he slams with his torso before Super Smash:
Water park can be also a track based on Wario & Waluigi, but the ghost racer is Baby Luigi.So far, Mario Kart 8 contains more Wario tracks than any other: