I would say use Yoshi and the Classic Dragster.
Win 150CC special cup
win 2,700 races
Win 50cc Star Cup
win in 1st or 2nd in the cup
you have to win in first or second
You have to win first place on 150cc Special Cup
As you probably know, Mariokart consists of three engine types: 50cc, 100cc, And 150cc. "cc" stands for cubic centimeters of engine space, therefore 50 is slowest, 150 is fastest.
Get the Gold cup in all 50cc , 100cc and 150cc cups
You win all the cups in all the modes including mirror mode. But R.O.B isn't a very interesting character.
Mariokart wii
You win baby daisy on the 50cc not on a specific cup you have to gain star ranking for Mushroom, Flower, Star, and Special Cups
I'm pretty sure you can't, although it's very annoying, you can't. the only way is for both of you to have MarioKart, and to have unlocked the courses.