Level Select
At the title screen, hold down start and A and B. Once you see the level number you want displayed, release the buttons.

Start from the level you lost
When you get a game over screen, return to the title screen,then hold down A and B while pressing select 5 times, then press start.

Unlockables

Uranoid mini-game
Successfully complete all levels and save your friends to unlock the Uranoid option at the main menu.

Neith
Successfully complete Zone Z' in Quest mode.

Operon
Successfully complete Zone W in Quest mode.

Rhea
Successfully complete Zone V in Quest mode.

Artemis
Successfully complete Zone V' in Quest mode.

Happy Smiling background music
Successfully complete Eta-5 in Uranoid.

Captain Neo background music
Successfully complete Theta-5 in Uranoid.