For to have all maps: during the game put start, after , hold L and to do: A.Y.X.B.Y.X.
Battery secondary weapon:
Go the map where you select the room you are to play next. Somewhere along the line you will be allowed access to the tree outside the level, to race as a snail. Finish in the top three to receive a battery as a secondary weapon. It has unlimited shots and is very strong, but only seems to work on the Boss levels.
Extra multi-player levels:
Play through each stage on 1 player mode in each level (ex. beat all stages on the 1st level) to access a new multi-player stage.
Pause the game, then hold L and press A, Y, X, B, Y, X. If you entered the code correctly, you will hear music.
(L) A.B.X.Y.B.A= 99 heavy munitions.
(L) B.A.Y.X.A.B= Change machine gun.
(L) A.X.B.Y.A.Y= Repair your machine.
(L) X.A.Y.B.A.X= Heavy weapon.
When codes are activated, there is a song .
Codes run on the european version at 100%.
Pause the game, then hold L and press A, B, A, B, Y, X. If you entered the code correctly, you will hear music. Then, return to the room selection screen to access the single player snail race level.
If you complete all the missions, a secret extra mission will be unlocked, where you get to race around a garden as a snail
Pause and hold the L button and press A, B, Y, X, Y, X.
At the title screen, press A, A, A, B, B, B to launch the credits.
Access the Hidden level without finishing all missions:
Pause the game during gameplay and hold the L button then press A,B,Y,X,Y,X. You can now access the snail race level even without finishing all missions.