From the Super Mario Wiki
9-Volt's bedroom is the most frequently seen room, being the only one to appear up until Game & Wario. Since 9-Volt loves video games, his bedroom is scattered with video game consoles from the past and present. In Twisted!, 9-Volt invites 18-Volt to his house to play some NES. In Touched!, 9-Volt and 18-Volt play their latest games in his bedroom. In Smooth Moves, 9-Volt again invites 18-Volt to his house, but this time to play a Game & Watch. The house is the main setting of the Game & Wario minigame Gamer, hosted by 9-Volt and 18-Volt. 9-Volt's mode takes place inside his bedroom, while the house can be seen across the street during 18-Volt's mode.
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