When you start the game and the Tiburon screen appears press Down, A, X. Now enter the OPTIONS screen and enter the password "XTRM3K" to access the best Mechs in the game.
Enter all of the level passwords and the Unlimited Ammo code. Once you've done that, enter the password "MKWFLL" for invincibility.
Thrash your enemies with this set of passwords.
For unlimited ammunition, enter the password M1R0G3.