This morning, Nintendo announced more features for Mario Tennis Open, including a new mode for the game. In Ink Showdown mode, you play against your opponent while Piranha Plants shoot ink balls at the 3DS screen from the back. When this happens, you need to hit the ink balls before they hit the screen or it gets covered in ink, similar to the Blooper item in Mario Kart.
Additionally, Mario Tennis Open will also have unlockable characters, such as Luma, Baby Mario and Dry Bowser. These characters can be unlocked either by progressing through the game or using QR Codes. Finally, the game also has StreetPass feature by which you can play against AI characters based on people you encounter via StreetPass.
Mario Tennis Open will be released on May 20th.