To unlock You have to
The Sly Joker Beat the Pawn, Knight and Bishop series on Standard difficulty
The Stingray Beat the Pawn, Knight and Bishop series on Expert difficulty
The Queen Series Beat the Pawn, Knight and Bishop series on Expert difficulty
The Silver Thunder Beat the Queen series on Expert difficulty
The Falcon MK-II Beat the Pawn, Knight, Bishop and Queen series on Expert difficulty
The Fighting Comet Beat the Pawn, Knight, Bishop and Queen series on Master difficulty
The Jet Vermilion Beat the Pawn, Knight, Bishop and Queen series on Master difficulty with all ships
The Master Difficulty Beat the Pawn, Knight, Bishop and Queen series on Expert difficulty
Password screen
At the machine selection screen in grand prix mode, press L, R, Start, R, L, Select.
Jet Vermilion car
Go to the machine selection screen in grand prix mode. Press L, R, Start, R, L, Select to display the password screen. Go to the Nintendo Of Japan web site and enter your name exactly using the on-screen keyboard keys, then click on the "Confirm" button (furthest right). You will get a password which will allow you to get the top secret Jet Vermilion car. Enter that password in your game to unlock the car. There are also two other ways to unlock the Jet Vermilion car. One is to unlock all other cars and complete championship mode 255 times. The other is to complete every series on Master Class with all other racers.
Sly Joker car
Win the Pawn, Knight and Bishop tracks on the standard difficulty setting to unlock the Sly Joker car.
Falcon MK-II car
Win any set of tracks on the expert difficulty setting to unlock the Falcon MK-II car.
Fighting Comet car
Win the Pawn, Knight, Bishop and Queen tracks on the master difficulty setting to unlock the Fighting Comet car.
Silver Thunder car
Win the Queen tracks on the expert difficulty setting to unlock the Silver Thunder car.
Stingray car
Win the Pawn, Knight and Bishop tracks on the expert difficulty setting to unlock the Stingray car.
Silence: Open C
Complete a linked game with another Game Boy Advance using only one game cartridge.
Master difficulty setting
Win the Pawn, Knight, or Bishop series on the expert difficulty setting in grand prix mode to unlock the master difficulty for that series.
Demonstration mode
At the title screen, press Select.
In-game reset
While playing a game, press Select + Start + A + B.
Delete saved games
Hold L + R and turn on the Game Boy Advance. Select "Yes" at the prompt to delete your game saves.
Turbo start
At the start of a race The word "ready" flashes and beeps 3 times, and then on the 4th beep the race starts.
Try to follow this, where it says "A" that is when you hit and hold the Accelerate button.
Beep......Beep....A. Beep......Beep
You have to have your engine revving loud, but before the point where it breaks into a screeching sound when the race starts to get the boost