100 gems: V1S10NS
Turn enemies to sheep: SH33P
Turn game orange: SP4RX
Turn Spryo orange: SPYR0
Crash Party U.S.A
At the beginning, when you first turn on the gameboy, press and hold every button exept the directional arrows ( A, B, R, L, Start and Select ) until the screen turns white, then let go and you get to play the bonus game.
Password Mode
At the game mode screen, press L and R to activate the code entry screen, and enter the passwords bellow to enable their perspective cheats.
Find any checkpoint(a portal, moneybags shop or the entrance to the second part of the level) near a lot of gems. I would advise you to make a course leading from the checkpoint and then back to it. Collect all the gems there then go and enter the checkpoint you chose and come back out straight afterwards (go through the portal then back through, go into moneybags shop and exit it or, go to the second part of the level and back through the passage way). The gems will have reappeared but you haven't lost any. Repeat this to get more and help you get all the collectors cards.
Various Codes
Press L + R at the "Mode" menu, then enter one of the following codes.
Code - Result
B41S0KV - Flying sheep instead of flame
g3mz - Grey game
SP4RX - Orange game
SPYR0 - Orange Spyro
p0rt4l - Purple game
s0yb34n - Rare "o sheep" card
v4n1ll4 - Rare "stone riptoc" card