One versus...One?

One versus...One? is the fifteenth mission in Mario Tennis Aces, taking place in Snowfall Mountain.

Layout
Mario and Toad suddenly notice that the train they are riding has unexpectedly stopped. While the Penguin conductor is investigating, a Shy Guy appears and tells the duo that the problem is coming from the summit, and challenges Mario to a tennis match if he wants to know more.

In this mission, Mario must play a three-set match with the Shy Guy. Several Goombas, Koopa Troopas, and additional Shy Guys pass by the court during the match; if Mario or the Shy Guy hits one of them, the ball loses most of its speed.

Afterwards, the Shy Guy reveals that he saw a treasure chest up at the summit, and warns Mario of a monster guarding it.

In-game text

 * "Defeat the Shy Guy while dodging the passengers!"