SEGA Superstars Tennis

For this start up a local singles match against the COM, set the match to as many rounds as you can and try to build up your star meter and enter superstar mode as much as possible. Doing it 10 times in the match will get you the achievement.

A good way to boost it quicker is, if you have a full star meter, try to not use it until after you have hit a ball that you know is going to score you a point - because you have effectively wasted it, you will be awarded half of your star meter back on the next go.

There is an easy way to get this using 2 controllers. Set up a singles match with any 2 characters you want. Set "Games" to 0 games - Tie Break, and Sets to 1. You can set games higher if you want to be cautious, but you shouldn't need it.

Now, do nothing. That's right, let the computer auto serve every few seconds and drop aces. (This is also great for the 100 Aces achievement.) Every 2-3 serves, you'll notice that your star meter is full. Serve and hit your star power. That's 1. Service will switch every 2 points. You should be able to activate your power each time you serve during the tie breaker.

Just make sure neither player returns a serve and the tie-breaker will go on as long as needed. The 10 star power and 100 aces achievements both pop during the match, so there's no need to finish the match.

You can speed this up quite a bit by actually playing both controllers, serving and canceling out of animations.

The easiest way to get this achievement is to play a singles match with two speed characters (I used Sonic and Shadow). There are a few ways to fill your star for superstar mode: rally the ball back and forth (which is why speed characters are suggested) or win the point.

The match settings i used were
6 games
5 set match
server: back (com has first serve)
com level: normal (so that he can return the ball to me without posing too much of a threat)

Put the game at deuce (40-40) and gain advantage by winning, then lose it. When you have a full star meter, wait until the COM is serving to you, and purposely miss it, and go into superstar mode. This will save about half of your star meter.

You do not have to play through the entire game. The achievement will pop as soon as you enter superstar mode for the 10th time. Alternatively, you can play against an easy level COM and beat it to a pulp, but be careful with how many games/sets you have remaining.

*edit* There is an option in the settings menu "fast star power" or something like that (i forgot) but it does NOT increase the rate at which you gain star power. It only cuts out the animation of activating the star power. So I would suggest just not bothering with it. It's easier to keep count if you are absolutely sure your power activates.