Zeargo

Ok well when your doing mirror, it's a good thing to just learn the tracks in the opposite direction, so than you know what to do. Or just remember the original track where up ahead you usually turn right, instead you turn left.

Its also a good idea to learn Snaking, because that can really help you a lot on races. It doesn't really work on the rainbow course so don't bother trying it there. Anyway the good combos is anyone with the Karts, Yoshis Egg Kart or Dry bones tank Kart. (forgot names but that should give you easy information). There really popular too. When you going to play the Cup with the rainbow course, watch out, because you might get knocked off by heavy karts. If you can't avoid this probably and get back into the race, try slowly being last or choose the normal standard kart that everyone has from drybones, Luigi or Yoshi.
Luigi's Poltergust 3000 is good also, but it's a tough one to handle unless your a pro at it.

Anyway, I hope that helped you.

myupwnsu

Dry Bones' tank is the best kart for almost all of the stages. I used him and I passed all cups in 150 and mirror easily. If you use the tank though do not rely on drifting or "snaking" at all because his handling is really good.

CrAzYDaX

I would recommend either Toad in Egg 1 of Luigi in dry bones.