Players of Mario Tennis Aces can add Petey Piranha and Shy Guy to their roster by participating in a singles and doubles tournament respectively.

Both of these characters were initially announced during a September Nintendo Direct and will be obtainable from December 1, 2018 to January 1, 2019 by participating in a specific online tournament. Petey Piranha is a powerful playing type who will be a participating bonus for Singles online tournaments throughout the month of December. Meanwhile technical player Shy Guy will be a participation bonus for those who play in a Doubles online tournament during December. Online play does require a Nintendo Switch Online subscription. Those without will have to wait until after January 1, 2019 to obtain these characters.

Shy Guy's super shot has him ascend via the usage of balloons, while Petey summons tornadoes to help help him shoot. Petey also does not utilize a racket, instead opting to use his large leaf-arms to slap the ball across the net. Petey's relative, the classic Piranha Plant, is making waves as the latest character to be announced for Super Smash Bros. Ultimate.

These characters round out the previously announced characters such as Diddy Kong, Birdo, Koopa Paratroopa, and the upcoming Luma, Boom Boom, and Pauline characters. You can check out the character trailers for both Shy Guy and Petey Piranha below.