Codes for Chu Chu Rocket:

Unlock Chao in the game
Remember the chao in Sonic Adventure? How cute (or annoying) they were? well, if you beat all 25 levels in Stage Challenge Mode you can have the Chao from Sonic Adventure replace the Mice.

Unlock NiGHTopians in Puzzle mode
Complete all 25 Mania puzzles.

The NiGHTopians are the "A-Life" creatures from the classic Saturn game "NiGHTS".

Unlock hard mode
Complete all 25 Normal mode puzzles.

Unlock mania mode
Complete all 25 Special mode puzzles.

Unlock special mode
Complete all 25 Hard mode puzzles.