Nintendo announced Mario Tennis Ultra Smash at its e3 Nintendo Direct. It's due for release on Wii U in Q4 2015.
Few details were revealed, other than it looks a lot like Mario Tennis, including power-ups such as a big mushroom.
This is what Nintendo PR had to say about the game.
"Up to four players can compete in tennis matches that could only take place in the Mushroom Kingdom. With the addition of Jump Shots to hit high balls overhead, or Giant Mushrooms that when picked up make characters bigger, this Mario Tennis is reborn with features enabling players to aggressively go after higher balls. The game is scheduled to launch in Q4 2015."