The challenges of each cup

Mushroom cup: Koopa beach 1
Star cup: first try (probably vanilla lake 1)
Shell cup: donut plains 2
Blue shell cup: Koopa beach 2
Golden mushroom cup: ghost valley 3, bowsers castle 3, rainbow road
Red shell cup: i literally first try max pointed this (Probably bowsers castle 1)
Banana cup: boo lake, cheese land
Leaf cup: cheep cheep island
Mega mushroom cup: bowsers castle 3
Lightning cup: rainbow road

I tried the Blue Shell Cup yesterday, and I gotta say, it's very annoying how I can't control my kart on Koopa Beach 2 half of the time, the CPU's always avoid the deep water, and it feels like luck if I even get in the top 4.

Then win by luck. Stay in the lower ranks and get items that will let you keep control over the water. Free win

That was the strategy I used and it eventually worked (along with learning how to control In water)

Thanks for the tip. It helped me get first, and after I completed the DS Star Cup, I can now play as Hammer Bro. (But I'll never use him because he's not Daisy.)