There are three ways of doing a harder serve:
1.) Press A and B simultaneously to serve.
2.) When it’s your serve, throw the ball with A, wait for 2 seconds and then smash it with B. If you did it right, you’ll hear a whistle.
3.) When it’s your serve, throw the ball up with A (or B), wait for 2 seconds and then smash it with Up+A.

i’ve been trying to hit aces, but can’t ever pull it off. i would like to get to the point that i can hit them every serve (or as often as the game allows me), but i can’t seem to do even 1.

does anyone have any tips that work for them? i’ve tried counting and timing but i just can’t seem to find that sweet spot.

Hitting aces in Mario’s Tennis for the Virtual Boy is definitely challenging, and I don’t believe there is any simple way to do it. I’m rather confident that hitting A and B simultaneously does not have a different effect on the serve in this game. It does in the later games, but not in this first one of the series. You always want to use the A button to hit fast and hard serves. Not only does hitting ace serves require great timing when hitting the ball after you toss it up in the air, but it also requires great original positioning of your character on the court for the start of the serve as well as the correct pressing of the L pad during the serve. When you are serving on the right side of the court, you want to move your character as far to the right as is safely possible. The reason why I say “safely” is because the more you are to the right at the start of your serve, the easier it is to hit the ball more to the left and on the boundary line, but you can hit it so far to the left if you are too far to the right that it will go out of bounds during the serve and you will get a fault. To get ace serves in this game, you always want to try to hit the ball as hard as possible and as barely on the boundary line and in such a way that it will go as far in the out of bounds direction after landing on the line as possible. How far the ball goes to the left during the serve also depends on how long you hold down left on the L pad during the hitting of the ball. If you just hold it for a little bit while hitting the ball, it will go just a little to the left, but if you hold left down the whole time, it will go as far to the left as it possibly can based on your original starting position on the court. If you want to be able to hold left on the L pad the whole time to make it easier on yourself, then you will need to find the correct starting position for your character for the serve, so that you will just barely land the ball on the line when you hit it full force while continuously holding down left on the L pad. All of these explanations hold for when you serve on the left side of the court, but obviously each of the directions are the opposite. The problem with all this is, if you don’t hit the ball full force, then it won’t land on the spot of the boundary line that you want. Hitting it perfectly full force is definitely difficult in this game, and I like that. There is nothing more to it than finding the right timing of hitting the A button again after you release it, but it takes a lot of practice to find the exactly right timing, and even once you find it, it is hard to do it successfully all the time. The timing being off any little bit will have a large impact on the serve. I like this fact since it simulates tennis more realistically than the later games. In the later games, I can always hit best possible serves whenever I want, and it shouldn’t be so easy to do so in my opinion.