Cheat: UFO Ending
Silent Hill 2's UFO ending is part of a tradition that started in the original Silent Hill and has continued with almost every installment since. Getting it in SH2 isn't too hard, though you can only get it in the Greatest Hits and Xbox versions of the game.
To see the UFO ending, you need to beat the game once plus the Maria scenario. Start a new game and you'll find yourself in the restroom once again. Look around and pick up the blue gem. You need to use the gem in the following places: 1) The Brookhaven Garden after fighting the hanging men, 2) in front of the row boat on the dock after leaving the meat locker, and 3) in Room 312 before you watch the tape.