To get a free power-up, pause the game and press: UP, UP, DOWN, DOWN, LEFT, RIGHT, LEFT, RIGHT, X, CIRCLE.
Pause the game and press Up, Up, Down, Down, Left, Right, Left, Right, X, Circle.
After you complete the Gradius 4 game, you unlock two things: You get Boss Rush, and also the Stage Select ability.
If you complete the Gaiden sub-game on normal or higher difficulty level, you unlock the Stage Select ability to start the game on any stage.
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