From the Super Mario Wiki
Emerald Street is a location in Diamond City that appears in 18-Volt's story in the Twist League in WarioWare Gold. Emerald Street contains a shop. In 18-Volt's story, 18-Volt, 13-Amp, 9-Volt, and Ralphie are seen on Emerald Street. The rap 18 x 13 takes place on Emerald Street with several lights being set up. In the game's credits, Emerald Street is seen in front of an image of 13-Amp and 18-Volt.