Instructions
Create a Mii by accessing the "Mii Channel" in the Wii system's start-up menu. Miis feature customizable facial features and body types. Once complete, name and save your Mii.
Insert the Mario Kart Wii game disc into the system and begin the game. Create a profile. Every profile will have a Mii character tied to it.
Beat the 100 cc Special Cup with any character to unlock the first Mii.
Unlock all 32 ghost data in Time Trials to unlock a second Mii. The Miis perform similarly, but wear different outfits.
Return to the character selection screen and both Mii racers will now be selectable for use in any single-player or multi-player mode, as well as online.