Go to the mini Chanel. You have to edit your mini.
Chat with our AI personalities
Go on the Mii Channel on the Wii home Menu and edit your selected Miis size so that he is quite big and then go back on to Mario kart wii and look at your mii. He or she will be an adult mii.
To Unlock Mii in Mario Kart you have to come 1st in the 100cc Special Cup. Or to Unlock the Other Outfit for the Mii you can unlock all 32 Expert Staff Ghosts.
Mii voices depend on gender, size, and color. Keep experimenting and eventually you will find one you like.
My favorite character is (Mario)Luigi. But really, it is my Mii!
There are only the normal Mii outfit, and there is a Mii (Mario) plumber suit. Those are the only suits I know of.