How to Unlock All Characters in Mario Kart Wii
If you want to unlock characters in Mario Kart Wii, unlock Baby Daisy by getting at least 1 Star Rank for all 150CC or 50CC Grand Prix Cups. For Baby Luigi, you need to race in 10 races, or win 100 Wi-Fi Ghost Races. To unlock Birdo, play Time Trials on 16 different courses, or win 250 Wi-Fi races. You can also get Bowser Jr. by getting at least 1 Star Rank for all 100CC Retro Grand Prix Cups, or race in 50 races. Additionally, unlock Diddy Kong by winning the 50CC Lightning Cup, or racing in 450 races.
Get at least 1 Star Rank for all 150cc or 50cc Wii Grand Prix Cups or race in 1,950 races. . Unlocks Baby Daisy. Win first place in the 150cc Special Cup or race in 2,850 races. . Unlocks Daisy. Unlock 8 Expert Staff Ghost Data in Time Trials, win 100 Wi-Fi Ghost Races, or race in 10 races. . Unlocks Baby Luigi. Play Time Trials on 16 different courses, win 250 Wi-Fi races, win the Star Cup or race in 1,350 races. . Unlocks Birdo. Get at least 1 Star Rank for all 100cc Retro Grand Prix Cups. . Unlocks Bowser Jr! Get at least 1 Star Rank for all 150cc Wii Grand Prix Cups. . Unlocks Dry Bowser. Win the 50cc Lightning Cup or race in 450 races. . Unlocks Diddy Kong. Win the 100cc Leaf Cup or race in 1,050 races. . Unlocks Dry Bones. Win the 50cc Star Cup or race in 750 races. . Unlocks King Boo. Attain at least 1 Star Rank for all Mirror Grand Prix Cups, race in 4950 races, or race in 50 races and have Super Mario Galaxy game files saved to your Wii and make sure you have saved the file of the Mii you have in Mario Kart Wii. . Unlocks Rosalina. Win all 150cc cups. Beat 18 Staff Ghosts. This will also unlock Rosalina. Play Time Trials on all 32 different courses, win 1,000 Wi-Fi races, or race in 2,550 races[11]
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Research source
Munson, T, (2009), "Video Game Master: Surefire Strategies", ISBN 0-545-17658-1

. Unlocks Toadette. Win the 100cc Special Cup. Unlocks Mii (Outfit A). Unlock all (32) Expert Staff Ghosts in Time Trials or win 5000 Times In Nintendo WFC. Unlocks Mii (Outfit B). Unlock 4 Expert Staff Ghosts in Time Trials, win 25 Wi-Fi races, or play 2,250 games to unlock Funky Kong!  
Get at least 1 Star Rank for all 150cc or 50cc Wii Grand Prix Cups or race in 1,950 races. Win first place in the 150cc Special Cup or race in 2,850 races. Unlock 8 Expert Staff Ghost Data in Time Trials, win 100 Wi-Fi Ghost Races, or race in 10 races. Play Time Trials on 16 different courses, win 250 Wi-Fi races, win the Star Cup or race in 1,350 races. Get at least 1 Star Rank for all 100cc Retro Grand Prix Cups. Get at least 1 Star Rank for all 150cc Wii Grand Prix Cups. Win the 50cc Lightning Cup or race in 450 races. Win the 100cc Leaf Cup or race in 1,050 races. Win the 50cc Star Cup or race in 750 races. Attain at least 1 Star Rank for all Mirror Grand Prix Cups, race in 4950 races, or race in 50 races and have Super Mario Galaxy game files saved to your Wii and make sure you have saved the file of the Mii you have in Mario Kart Wii. Win all 150cc cups. Play Time Trials on all 32 different courses, win 1,000 Wi-Fi races, or race in 2,550 races[11]
X
Research source
Munson, T, (2009), "Video Game Master: Surefire Strategies", ISBN 0-545-17658-1

. Win the 100cc Special Cup. Unlock all (32) Expert Staff Ghosts in Time Trials or win 5000 Times In Nintendo WFC. Unlock 4 Expert Staff Ghosts in Time Trials, win 25 Wi-Fi races, or play 2,250 games to unlock Funky Kong! 