Halo: Combat Evolved Cheats
Note: This only works in co-op mode.
On level 8, when you are about to destroy the second generator one player must stay outside the room while the second goes in and destroys the generator. Once it's gone the player who stayed behind will be teleported to where the generator stood, and the Flood which would have attacked you on the way out will have teleported with him - only now they're all frozen and you can make your escape without having to fight them.
To reload most weapons faster, press X, then shortly after that press B to melee.
Note: For the shotgun this will cause you to stop reloading all together.
At the main menu hold down the Back Right button and press:
B, X, Y, A, A, A, B, X, Y, Y, Y, B, B, Y, and Start
In any level press Start, and at the menu hold Right Trigger and press:
X, X, White, Black, A, Y
Note: To confirm correct entry of this code, a voice will say confirmed.
There is a secret cave on level 5 at the button of the map entrance. It comes out on the side of the enemies, where they are not expecting it.
Beat any level on legendary and you will get new enemies
Successfully complete the game in campaign mode on the legendary difficulty setting to view a different and longer ending sequence.
When a Dropship unloads aliens, the next dropship will hover in the air. If you take your sniper rifle and zoom in on the sides of the dropship where the doors open, the aimer will turn RED. Fire once or twice and the alien will fall to the ground.
If your going to use a plasma grenade, throw it at the alien where it sticks onto them. It will make sure it kills the alien. The aliens can do this to you if you don't move quickly enough.