Don't hit each other in the game, or give a chao a hat as the second character, or the game will freeze. Hold the D-Pad up when selecting a stage in 2P mode.
This code, while turned on, will enhance your chao's second evolution. It does eventually shrink, but as long as the code is turned on, then there is a way to make it big again: do something for it to get a heart, such as giving it a full fruit, picking it up, petting it, etc. You could also leave the garden and come back, and it would be big again. This code also evolves any un-evolved chao, even if they just hatched!
Max Rings- Chao Garden
EWUW-4XF0-6YT1E 7738-KBH6-NN2H9
Resets every time you visit the shop and/or reload the game.