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Playstation - Galaxian 3 cheats

Ghost player (duplicate yourself)
Enter to the play record screen and enable that feature. Begin a new 
game and play as far as possible. Go to the gunner battle option and 
push Right, Right to choose the "Ghost" option. Begin another game 
to have your self as a partner. 

Enable Debug mode
Push L1, R2, R1, L2, Up, Down, Up, Down while the Namco logo flying
on the screen.