Mario costume
To get the Mario costume for your mii, you must unlock ALL 32 expert staff ghosts in time trials. (To make sure you get it, make sure you beat the staff ghost first by 4 or 5 seconds, and then a message saying " a fast staff ghost has appeared!" on the bottom of the screen will show.)
More tricks, tips and cheats for this game are right here - Mario Kart Wii cheats
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