Here is a list of items, karts, characters, and more that you can unlock.
 100CC Karts Unlockable
- To unlock the ability to drive karts in 100cc cup races, earn all of the trophies on each 100cc cup race.
 50CC Race Bikes
- To unlock the ability to drive bikes in 50cc cup races, earn all of the trophies on each 50cc cup race.
 Unlockable Characters
- Baby Daisy: Get a one star rank or better in all 50cc Wii cups.
- Baby Luigi: Unlock eight expert staff ghost data in Time Trials mode.
- Birdo: Play 16 different courses in Time Trials mode. Alternately, get 250 WiFi wins.
- Bowser Jr.: Get a one star rank or better in all 100cc Retro Cups.
- Daisy: Win the 150cc Special Cup.
- Diddy Kong: Successfully complete all 50cc Retro Cups or get 450 race wins.
- Dry Bones: Win the 100cc Leaf Cup.
- Dry Bowser: Get a one star rank or better in all 150cc Wii Cups.
- Funky Kong: Unlock four expert staff ghost data in Time Trials mode.
- King Boo: Win the 50cc Star Cup
- Mii (Outfit A): Win the 100cc Special Cup.
- Mii (Outfit B): Unlock all 32 expert staff ghost data in Time Trials mode.
- Rosalina: Get a one star rank or better in all Mirror Mode Retro Cups. Alternately, have a saved game file from Super Mario Galaxy and win a number of races.
- Toadette: Play on all 32 courses in Time Trials mode. Alternately, get 1,000 WiFi wins.
- Leaf Cup - Earn trophies in the Shell Cup and Banana Cup
- Lightning Cup - Earn a trophy in Leaf Cup
- Special Cup - Earn a trophy in Star Cup
- Star Cup - Earn trophies in the Mushroom Cup and Flower Cup
 Mirror Mode
- To unlock Mirror Mode, you need to win all 150cc cups or play 4,950 races or more.
 Unlockable Vehicles
- Piranha Prowler (Large Kart) - Win the 50cc Special Cup
- Turbo Blooper (Medium Kart) - Win the 50cc Leaf Cup
- Cheep Charger (Small Kart) - Earn at least a 1 star rank in all 50cc Retro cups
- Rapide (Medium Bike) - Win the 100cc Lightning Cup
- Twinkle Star (Large Bike) - Win the 100cc Star Cup
- Nitrocycle (Medium Bike) - Attain at least a 1 star rank in all 100cc Wii Grand Prix cups
- Royal Racer (Medium Kart) - Win the 150cc Leaf Cup
- Quacker (Small Bike) - Win the 150cc Star Cup
- Dragonetti (Large Kart) - Win 150cc Lightning Cup
- Dolphin Dasher (Med. Bike) - Win Mirror Star Cup
- Phantom (Large Bike) - Win Mirror Special Cup
- Bubble Bike (Small Bike) - Win Mirror Leaf Cup
- Blue Falcon (Small Kart) - Win Mirror Lightning Cup
- Rally Romper (Small Kart) - Unlock an expert staff ghost data record in Time Trial mode
- Aero Glider (Large Kart) - Earn at least a 1 star ranking in all 150cc Retro cups
- Torpedo (Large Bike) - Unlock 12 expert ghost data records in Time Trial mode
- Magikruiser (Small Bike) - Play Time Trial on 8 courses.
 Alternate Title Screen
- To unlock an alternate title screen that will be shown when the game starts, win each and every cup available in the game.
 Star Icon When Playing Online
To obtain the star icon, you must complete all Grand Prixs(50cc, 100cc, 150cc, and Mirror) and obtain at least a 1 Star rank on all cups of each Grand Prix. If you obtain a Star rank in most cups and obtain a letter rank in the few remaining Cups, your lowest letter rank will be your Overall Rank
If completed, then, when playing online, your opponents will be able to see your star icon when racing and in the results.
You can also get 2 star and 3 star icon online using the instructions said above.