Easy... you need to go to 1 player - Time trials and race against ghosts. Once you beat a fair number of them, you'll get staff ghosts. Once you beat a fair number of those, you get your outfit.
It's just your mii wearing overalls like mario's. :)
You can't change their clothes, only the color of them.
unlock all 32 expert ghosts in time trials.good luck!
There is no way to unlock it. Because it does not exist.
No it's fake because you can't get 15000 points. Maybe wIth a hack you can get that many points.