Nintendo promised that the highlight of the new Nintendo Direct presentation would be Mario Tennis Aces, and they didn’t lie- they did spend quite a bit of time on it in the new video, showing off gameplay (including multiple different power ups and perks), control options (including motion controls and gyro), game modes (including a classic mode where you can turn off all the additional power ups and just play regular tennis), and online functionality (including a tournament mode with matchmaking).
They also confirmed that the game will be getting an online tournament for players to play before the game launches- so basically a beta for you to take the game for a spin for yourself and see if it is something that appeals to you.
As for when it is launching- well, we have a release date for that as well. Mario Tennis Aces launches exclusively on the Nintendo Switch on January 22.