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Playstation - Gradius Gaiden cheats

Unlock level select option:
Finish the game without using a single continue in normal mode.
to unlock level select option at the title screen.

Get Power-up
Pause the game play and push Up, Up, Down, Down, Left, Right, 
Left, Right, X, Circle. Sound will confirm the correct code entry.
Note: You can use this cheat only once per level.

Unlock free play mode
Play with the game minimum 10 hours total then save the game. 
After that, restart the game to unlock free play mode.