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Sony PSP - Gradius Collection cheats

Unlock all weapons and power-ups:
While playing under the easier difficulty level, pause the game, then
press Up, Up, Down,  Down, Left, Right, Left, Right, L, R. 

Unlock all weapons and power-ups in the Japanese version of the game:
While playing under the easier difficulty level, pause the game, then
press Up, Up, Down, Down, Left, Right, Left, Right, X, Circle.


Gradius 3: 
Unlock Cube Attack: Survive until level 9. 
Unlock Gradius level: Intentionally get shot by the Final Boss. 
Unlock Salamander level: Intentionally get shot by the Final Boss. 
Unlock Stage Select option: Finish the game. 
Unlock Extra Mode: Survive until level 9. 
Unlock Extra Edit: Finish the game. Select Extra Mode to access more weapons. 


Gradius 4: 
Unlock Boss Rush mode and Stage select option:
Finish the game once. 


Gradius Gaiden: 
Unlock Stage select option:
Finish the game on normal or higher difficulty level.