Mario Kart Wii/Characters

Light Weight

 * Toad
 * Koopa Troopa
 * Baby Mario
 * Baby Peach

Middle Weight

 * Mario
 * Luigi
 * Peach
 * Yoshi

Heavy Weight

 * Wario
 * Donkey Kong
 * Bowser
 * Waluigi

Unlockables
Warning, Spoilers Ahead

Light Weight
How To Unlock: Unlock 8 Expert Staff Ghost Data on Time Trials.
 * Baby Luigi

How To Unlock: Attain at least 1 Star Rank for all 50cc Nitro Grand Prix Cups.
 * Baby Daisy

How To Unlock: Attain a Gold Trophy in the 100cc Leaf Cup.
 * Dry Bones

How To Unlock: Play on all 32 courses in Time Trials.
 * Toadette

Middle Weight
How To Unlock: Attain a Gold Trophy in 150cc Special Cup.
 * Daisy

How To Unlock: Attain Gold Trophies in all 50cc Cups.
 * Diddy Kong

How To Unlock: a) Beat 250 people while playing online.              b) Play on 16 courses in Time Trials.
 * Birdo

How To Unlock: Attain at least 1 Star Rank for all 100cc Retro Cups.
 * Bowser Jr.

Heavy Weight
How To Unlock: Attain a Gold Trophy in 50cc Star Cup. How To Unlock: a) With a Super Mario Galaxy save on your Wii, attain Gold Trophies in all of at least one series of Cups.             b) Attain at least 1 Star Rank for all Mirror Retro Grand Prix Cups.
 * Boo
 * Rosalina

How To Unlock: Unlock 4 Expert Staff Ghost Data in Time Trials.
 * Funky Kong

How To Unlock: Attain at least 1 Star Rank in all 150cc Nitro Grand Prix Cups.
 * Dry Bowser

Miscellaneous
How To Unlock: Attain a Gold Trophy at 100cc Special Cup.
 * Mii (Outfit A)

How To Unlock: Unlock all Expert Staff Ghost Data in Time Trials.
 * Mii (Outfit B)

Spoilers Finished