Mario Kart Wii Gecko Codes, Cheats, & Hacks

Hi. I have been told that the only way to get a Mii to load in Mission Mode is by using the Force Character Code. But every value for a Mii that I've used on it just crashes the game. Could a code be made that forces every character to be a specific Mii from your console? That would help a lot.

Also, would it be possible to somehow make each CPU be a different Mii from your console? That would be helpful as well.

I need to find more about it.