Just win good trophies in enough races first, and it should unlock characters and the cups!
First beat 150cc. You should of unlocked 150cc mirror. If you beat 150cc mirror you unlock R.O.B.
Daisy
Get one star rank or better on all 150cc cups.
You have to win first place on 150cc Special Cup
150cc Lightning cup.
star rank on all 150cc grand prix cups
To unlock dry bowser, you nedd to beat the first 4 cups on 150cc with one star or better.
you get first in the 150cc leaf cup
you get gold on every thing 50cc-150cc.when you get gold on the lightning cup on 150cc you unlock mirror.
to unlock dry bowser, you need to get a one star rank or better in all 150cc Wii cups (all the cups on the top)
Win 150CC special cup
Finish 150cc Mirror Mode,With gold trophies on all cups... how to unlock 150cc mirror mode: Finish 150cc Retro Class with Gold trophies on every cup