get the gold cup in 50cc lighting cup.
win the 50cc lightning cup to unlock diddy kong
Win all the 50cc cups.
Win the 50cc lightning cup
unlock 4 expert staff ghost data in time trails mode
---- === === ---- === ===
there is no cup to unlock Diddy Kong you must go on the same account like 180 times (or more, i don't know) and it'll tell you that you unlocked Diddy Kong.
If you need to unlock her in Mario kart wii here is the answer: Win the 150cc Special Cup. If you need to unlock her in Mario Kart 7 here is the answer: Win the 150cc Mushroom Cup. Source: I beat Mario Kart Wii, and I unlock Daisy in Mario Kart 7.
In Mario kart wii you have to win the 150cc special cup
By doing it
No
Here are a list of the most easiest people to unlock that I know of: Birdo: Race 16 Corses On Time Trails Diddy Kong: Get A 1 Star Rank Or Over On All 50cc Grand Prix King Boo: Win 50 Races That's everybody I know for now!
Win 100cc Lightning Cup.