How do you get new characters?

[Bastoise99]

?
Do you just beat different cups?

And also, does your grade on a race matter at all in Grand Prix, or Mission mode?

 

[PrinceBoo]

To get new characters, just win gold on all the cups in Nitro Grand Prix and
Retro Grand Prix. Do all of them on 50cc 100cc and 150cc and youlle unlock
lots of stuff as you do that

 

[Kyle]

Spoiler for unlocking karts!













To be more specific...

50cc Nitro = Dry Bones
50cc Retro = Daisy
100cc Nitro = 3 karts usable among characters unlocked
100cc Retro = Walugi (100cc's might be mixed up)
150cc Nitro = 7 Karts usable among characters
150cc Retro = I dunno, but I'm guessing mirror mode since you unlock R.O.B in mirrior mode, and you cant win him/her in regular racing.

and yes......gold cups are need for all 4 Grand Prixes (grades dont much matter)