Cheat Method 2 (Used on some versions??)
During gameplay press F1 to get the console then put in a code below hit ENTER then press F1 again to activate
cht_bGiveAll - Get all weapons
cht_bGod - Invincibility
cht_bInvisible - Be invisible
cht_bRefresh - Max Health
cht_bFly - Fly Mode
cht_bGhost - No clipping mode
Mega Secret On First Level
On the first level when you start of in the teleport turn around you should see a ramp go down it and turn right you should see a door way open it inside it has about 4 guys in serious Sam shirts with really big heads you can kill them if you like plus there is some rockets have fun
Hippie Splatter Art
What you do first for this funny cheat is set the blood and gore on hippie mode. Then, you go to a level where you encounter beheaded bombers. As soon as you encounter them, hit the ~ button, (to the left of the #1 button on your key board) and type in "please fly". You will be able to fly! Simply fly into the air, and the headless freaks will group under you, just shoot one and they will all blow to pieces, painting a mural on the ground. I apologize for this being so long, but try it, it's a lot of fun.
Bring up the console using the ~ key then put in one of the following codes:
please fly - flight mode
please ghost - No Clipping mode
please tellall - Shows Netricsa messages
please refresh - ???
please giveall - All items
please god - Invincibility
please open - All doors opened
please invisible - Invisibility
please killall - Kill enemies
Get any level
When in Serious Sam, hit new game. Then go to custom levels. It should list every level in the game. Simply click on one and you will be transported there. Another cool thing about this is that you have any weapons that you normally picked up on the levels you skipped.
Get the Heart Without Getting Caught!
OK. First, go to the Tomb of Ramses III, then, later on in the level, there is a cage with a heart inside. Get in line with the heart, or one of the four entrances. Push up on the joystick as hard as you can to get to the heart inside the cage. As soon as you get the heart (you'll need reflexes for this part) back out as fast as possible. Then, instead of being caught in the cage, you will be free!
Kill Enemies Fast and Keep More Health
Ok this isn't really a cheat but on levels were you fight those little green things as a boss use your chainsaw and you will kill them faster and you will keep more health then using any weapon or wasting any bullets.
In the main menu click and hold the left analog-stick, while holding it press BLACK, WHITE, then Y. If done right a cheat menu will apear at the main menu.
How to unlock Mental Mode
Finish the game one time using Serious Mode. mental Mode makes enemies phase in and out