Watch the credits and click all lines that have the letter "O". A sound will confirm each correct click. When the name list ends, wait and another list will begin. Once again, click the lines that have the letter "O". The word "Secrets" will appear. Click it to play the Alien Zoo Keeper mini game.
Start a game and do not shoot for about two minutes while not getting damaged by the aliens.
Successfully complete the game under the normal difficulty setting to unlock the hardcore difficulty setting and Typ 'o' Shooter mode.
Set the system date to December 25. When the game starts, a "Happy Holiday" message will appear with snow. Click on the snow or message to return to normal.
Have your first shot kill an alien with one hit. Walk directly to its body and wait at that location. Allow the other aliens to almost kill you to get the gun. Note: This only works in earlier versions of the game.