Since WarioWare: Twisted!, 9-Volt always stars together with 18-Volt in the WarioWare series, who becomes one of his best friends in this game.
As he appears in Super Smash Bros. Platformer as a playable character, these sound effects when 9-Volt jumps, runs, bounce, or attacks sounded similar to a cheerful creatures called LocoRoco when they Bounce, grow, or split apart. In the Adventure mode called The Tamagotchi emisarry, he joins along with 18-Volt,Suka Joe, and Sonic the Hedgehog as the trio who were save the Tamagotchi world.
He is it level "Game POWER!" in this game.