Cheat Mode:

Platform: PC

Hold [Left Shift], then press [F3] [F4] [F3] [F3] [F4] at the main menu. Then, press [F1] to display the cheat menu.
Cheat Mode (Alternate):

Platform: PC

Start the game as usual. Press ` (tilde) to bring up the console. Type sam_iEnableCheats=1 and press [Enter]. Close the console (press ` again) and then bring up the main menu by pressing (ESC). Access the cheat menu by pressing [F1].
Cheat mode (demo version):

Platform: PC

Press ~ during game play to display the console window, then type sam_iEnableCheats=1 as a case-sensitive code to enable cheat mode. Press ~ again, then press (Esc), followed by [F1] while in the pause menu. You can now select the cheat options.
Developer Cheat Mode

Platform: PC

If you want to use the developer cheats simply use the following command instead:
sam_iEnableCheats=2
Then use the following keys While playing:
[Y] - Ghost, go through walls
[G] - God mode
[U] - Auto aiming
[J] - Turbo, fast running
[I] - Invisibility
[L] - Fly mode
[K] - Kill all enemies on screen
[Insert] - Extra life
[PgUp] and [PgDn] - Chapter change
[[] and []] - Real time factor
You can also disable the cheats with:
sam_iEnableCheats=0
Removing the Cheat Status from a Saved Game

Platform: PC

Once you have saved the game with activated cheat mode you also need to remove the cheat status from the savegame. Go to:
.../Serious Sam 2/Content/SeriousSam2/PlayerProfiles/[Something]/SavedGames
and open the desired savegame with a text editor such as Notepad. Look for:
STAT_CHEAT="True"
and change this to:
STAT_CHEAT="False"
Save and start the game. The cheat status will now be deactivated with the beginning of the next chapter.
Difficulty Bonus

Platform: PC

Start a new game under the difficulty of your choice. At any time, go back to the main menu, select Custom Level, and play it through in Serious Difficulty. Load the game you had previously started, and although the starting difficulty will have stayed the same, at the end of each level you will get the difficulty bonus for Serious difficulty.
Get Rocketlauncher in the first level

Platform: PC

Before you go through the monkey head, look to your right. There should be a small waterfall.A little bit more right, there is a platform up on the wall. Shoot at the piece of wood under this, and a rocketlauncher will fall down.