Things You'll Need
Instructions
Turn on your Wii and begin playing. Make sure you have a save file from Super Mario Galaxy on your Wii's hard drive.
Participate in all of the circuit races once. After this, you will have raced 32 times.
Race on the "Luigi Circuit" track 18 more times. Since this track is easy and short, you should complete the races quickly. Once you have completed this step, Rosalina will automatically appear as a controllable character.