No CPU Cars
First highlight a track and then hold X + L.
Use the Second Horse
Hold L + R + Y + Z, then press A to choose a game mode on the main menu.
Use the Horse
Hold L + X + Z, then press C to choose a game mode on the main menu.
Use the Daytona super car
Hold R + X + Y + Z, then press C to choose a game mode on the main menu. 'The Hornet' will have changed, it will have 5 stars in every catigory.
Mirrored Tracks
Hold X+Y+Z and choose a track.
Jeffry Dance
On the Expert course, as you approach the Jeffry statue, Press the X button rapiddly so he turns, and stands on his head.
Race with Uma
When at the Main Menu, hold L + X + Z, then press C.