when/how do you unlock different karts/bikes in Mario cart Wii?

[clopdump]

I've gotten gold in every cup except mirror, ive only got flower and mushroom that's gold. and I dont have even close to every charactor in Mario Kart. Also how do you unlock really good karts/bikes like the B-Dasher?

 

[joryc94]

I went on Wi-Fi and unlocked some but do the mirror then try Wi-Fi.