Furd Herder mini-game:
Enter Green Alien, Green Alien, Square, Green Alien as a password to unlock a Minesweeper-like mini-game.

Snake mini-game:
Enter Circle, Diamond, Square, Green Alien as a password.

View Klax history:
Enter Yellow Alien, Pillar, Pillar, Green Alien as a password.

View Klax myth:
Enter Square, Pillar, Diamond, Green Alien as a password.

View programmers:
Enter Green Alien, Green Alien, Circle, Square as a password. Note: A Game Boy Printer is needed for this trick.

View credits:
Enter Pillar, Yellow Alien, Diamond, Diamond as a password.

Adventure mode (European version):
Enter Square, Yellow Alien, Green Alien, Yellow Alien as a password.