Mario Tennis Open, due out for your 3DS later this month, has a few mini-games available for your Mario tennis ventures. But one in particular lets you traverse the Super Mario Bros. world by hitting tennis balls at Goombas and coins.
Take a look at Elyas' preview of this mini-game in the video above, featuring my own 3DS. Look how pretty it is.
There seems to be a propensity amongst game developers working with iconized characters like Mario to see their creations live outside the realm of their natural universes. Mario with a tennis racket is no stranger to us, though.