As an unique feature, Mario Kart Wii allows players to use their Mii as a playable character in the game. The Mii is clothed with a full-body race suit. The color varies depending on whatever favorite color the Mii has been associated with on the main Wii menu.
In Mario Kart Wii, Miis are designated to a certain weight class based on their height when created. Miis are not equipped with any special weapons or features.
Miis are playable in regular play, versus play, battle mode and online mode.
As a secondary feature, Miis are spectators in some of the courses, including Coconut Mall.
Background
Mario Kart Wii is a kart racing video game developed and published by Nintendo for the Wii. It was first announced at E3 2007 in Los Angeles. Each copy of the game is packaged with a Wii Wheel, designed to house the Wii Remote in a way that allows more intuitive and conventional steering.
Mario Kart Wii Mii News, Blogs and Information
Mahalo's Guide to Mario Kart Wii
Wikipedia: Mario Kart Wii
GameTrailers.com: Mario Kart Wii Gameplay
NintendoWiiFanboy: Mii Integration and Online Menu
Wiis World: Wiis in Mario Kart Wii
YouTube: Mario Kart Wii Mii Outfit