The North American version of the game's case cover is reversible. Take it out of the case and look at the other side to see an alternate cover.

Successfully complete the stage under the hard difficulty setting with the unlimited ammunition option or choosing a weapon. If your score penalties were low and your total score high, the very hard difficulty setting will be unlocked. Do the same under that setting to unlock the next difficulty. The order is: very hard, aggressive, dangerous, execution, hopeless, nightmare, and champion.

While holding on with R1, press R2 and you can go up a bit higher.

To gain Unlimited fire power beat the game on easy Then you will unlock unlimited fire power and a choice of two weapons to start off with on each level and both of those will have unlimited ammo.