Cheat
Type L0SR at the password screen. You get a strange code. Start a new game or load a previous saved game.

To gain full energy and health
While playing press A + B + C

To gain full energy and health
While playing press A + B + C.

To get all weapons
While playing press X + Y + Z.

Levelcodes ( they only work in Easy Mode )
Level 02: FWQP
Level 03: PLRQ
Level 04: SZNF
Level 05: TD5S
Level 06: J1BT
Level 07: K2CV
Level 08: N3DW
Level 09: M4FX
Level 10: X5GZ
Level 11: C6HO
Level 12: D7J1
Level 13: F8K2
Level 14: FGL3
Level 15: JFM4