Extremely simple tennis game. The 3D helps a lot with ball position and is a novel idea for the hardware, but after 5 minutes the game starts to feel stale.

You can do a normal shot with A and a lob with B. If the opponent lobs the ball at you, you can press A or B while the ball is directly overhead to smash it back at them. That's it. Mario Tennis (the N64 one) introduced plenty of unique mechanics that set the series apart from other video-tennis games, but Mario's Tennis (this one) proceeds the N64 release by 5 years and has no unique spin on the game. It's literally tennis. If you still want to try Mario's Tennis I highly recommend playing as toad or koopa, as they have an automatic lunging move to hit tough shots.

I restored a virtual boy recently, and this was my go-to testing game since it was quick to start and was a simple game. However, if you own a modded 3DS, an emulator was released recently that allows you to play VB games with proper 3D support. The 3D effect is indistinguishable from the real thing IMO, and it also allows you to change the palette to whatever grayscale you prefer. If you're interested in playing any VB games at all, I highly recommend the Red Viper emulator!

Anyway, Mario's Tennis is boring. Go play the later entries.