Version 2.0 of Mario Tennis Aces drops today and brings with it the first of many limited time co-op challenges that you can take on with friends in order to unlock new outfits and new color schemes for the in-game characters. The current challenge is titled "Boo Hunt" and is available starting today until Thursday, October 11.
With the implementation of the Nintendo Switch Online Service today, you will need an active subscription to play this new co-op challenge with friends over the Internet. Fortunately, you can also play locally with four friends provided every one has their own Joy-Con as the challenge uses the "Swing Mode" mechanics where you swing the Joy-Con like a tennis racket. You can check out the full list of changes and updates in the patch notes over on the Nintendo Support site.
Mario Tennis Aces is available on the the Nintendo Switch. Two player couch co-op is supported in matches where you take on A.I. opponents, and four player couch co-op or four player online co-op is supported in the new Co-Op Challenges that last for a limited time. A Nintendo Switch Online Service subscription is required for online play.