This is an alternative method of unlocking characters, karts, and bikes. Simply play the required number of games (races/battles). This method takes a while, but is far easier to complete.

Unlockable	How to unlock
Baby Daisy	Play 1,950 races/battles.
Baby Luigi	Play 3,150 races/battles.
Birdo	Play 1,350 races/battles.
Blue Falcon	Play 4,200 races/battles.
Bowser Jr.	Play 3,450 races/battles.
Cheep Charger	Play 1,800 races/battles.
Daisy	Play 2,850 races/battles.
Daytripper	Play 2,700 races/battles.
Diddy Kong	Play 450 races/battles.
Dolphin Dasher	Play 3,750 races/battles.
Dry Bones	Play 1,050 races/battles.
Dry Bowser	Play 4,350 races/battles.
Funky Kong	Play 2,250 races/battles.
Honeycoupe	Play 3,000 races/battles.
Jet Bubble	Play 3,900 races/battles.
Jetsetter	Play 4,500 races/battles.
King Boo	Play 750 races/battles.
Magikruiser	Play 900 races/battles.
Mii Plumber's Costume	Play 5,100 races/battles.
Mii Racing Suit	Play 1,650 races/battles.
Mirror Mode	Play 4,800 races/battles.
Phantom	Play 4,050 races/battles.
Piranha Prowler	Play 600 races/battles.
Quacker	Play 2,400 races/battles.
Rosalina	Play 4,950 races/battles.
Shooting Star	Play 1,500 races/battles.
Sneakster	Play 3,300 races/battles.
Spear	Play 3,600 races/battles.
Sprinter	Play 4,650 races/battles.
Super Blooper	Play 300 races/battles.
Tiny Titan	Play 1,200 races/battles.
Toadette	Play 2,550 races/battles.
Zip Zip	Play 2,100 races/battles.