It is an outfit for your mii so you can use them in Mariokart
I looked up the game's data and there was data for every character. There were 4 Mii-files. Outfit A - male / Outfit A - female / Outfit B - male / Outfit B - female No sign of C anywhere. I had seen...
There isn't one.
unlock 32 expert staff ghosts in time trials
You have to unlock all 32 Expert Staff Ghost Data in Time Trials ...