It's the leaf cup, actually. Beat the flower cup.
On the character selection screen there should be a rectangle for miis. You can earn Outfit A by winning the 100cc Special Cup .
there is no hat cup
Beat the star cup
The Special cup
The Shell Cup, Banana Cup, Leaf Cup, and Lightning Cup.
Get a Bronze, Silver or Gold Cup in the Shell Cup and Banana Cup.
by getting gold on the star cup
Win 150CC special cup
By finishing the race's
win in 1st or 2nd in the cup
Win 50cc Star Cup
All you have to do is play the 50cc in the Star Cup.