Nintendo has just announced that they will release a demo of the game on June 1, and also run an online tournament starting the very same day. As you advance through the tournament stages you'll earn points based on your performance, allowing you to unlock another five additional characters to play with. Matches are playable online against other people around the world or in single-player against AI-controlled opponents, but in this trial you'll need to be connected to the internet at all times no matter which mode you play.
Finally, Nintendo will host a Mario Tennis Aces Japan Open 2018 U-12 event on June 23 and 24, where 128 elementary school grade participants can sign up to compete on a first-come, first-entered basis.
Lastly, those who participate in the online tournament will get Mario's "Overalls Mario" outfit for the full version of the game. It will be made available for Switch owners June 22 but there are going to be some test rounds a couple weeks ahead. Along with the announcement of the dates of the tournament, Nintendo released 2 new videos of its tennis game that you can check out below.
Mario Tennis Aces is due out June 22, but an online beta will kick off from June 1-3.