Mario Tennis Open (マリオテニス オープン Mario Tenisu Ōpun) is a Mario sports game for the Nintendo 3DS. The game was developed by Camelot, which has produced most of the previous Mario Tennis titles, not including the Virtual Boy Mario Tennis release.
Like earlier Mario Tennis titles, Mario Tennis Open incorporates characters, settings, and scenarios from the Mario franchise. Players can engage in standard tennis matches but also play special variants with different rules and objectives. Seventeen distinct playable characters are available, each with special qualities that are used to the players' advantage. Mario Tennis Open is also the first Mario Tennis game to feature simultaneous online play.
Source: Wikipedia, "Mario Tennis Open", available under the CC-BY-SA License.