Pause in any game under their easier difficulty setting, then press Up, Up, Down, Down, Left, Right, Left, Right, L, R. All weapons and power-ups will be unlocked. In the Japanese version of the game, press Up, Up, Down, Down, Left, Right, Left, Right, X, Circle.

Gradius IV has unlockables. You must complete the following tasks and finish your game. That means if you don´t die, you won´t unlock anything, even if you have a saved game after completing the task. You should be careful too: If you load a game without a now unlocked feature, you will lose it again if you finish your game:

Gradius III has unlockables. You must complete the following tasks and finish your game. That means if you don´t die, you won´t unlock anything, even if you have a saved game after completing the task. You should be careful too: If you load a game without a now unlocked feature, you will lose it again if you finish your game..

Put the ship in the middle of the screen, near the bottom. The blasts will be unable to hit you. Even better yet, this boss doesn't require you to actually damage it to a certain point, so just stay in this safe zone and it will die after 15 seconds or so.