Simply win a Tournament mode match in Xbox Live.
There are two things that make this achievement somewhat difficult:
1. It is time consuming. Even if planet wins is set to 2, you're looking at around a half hour of playing. Plus if you get unlucky and a CPU or your opponent beats you on one of the planets, you'll have to beat another one to win, increasing the time by quite a bit.
2. There is next to no one online anymore. Your best bet is to find a friend who has this game and arrange all of your online matches.
If you can manage to handle those, you should have minimal trouble trying to get this.