First of all start the game with the "-console -devmode" command line parameter. Then press [~] during game play to display the console window, then enter one of the following codes to activate the corresponding cheat function. Note: Keep in mind You cannot enable codes in online games. Also, commonly used commands can be placed in an "init.txt" text file in the main game directory that also contains the "halo.exe". Entries in that file should be made in the same format that they are entered into the console, and will be activated automatically when the game is started.
cheat_medusa <0 or 1> - Toggle instant deaths for enemies that see player
game_speed <0-20> - Set game speed
cheat_infinite_ammo <0 or 1> - Unlimited ammunition
cheat_super_jump <0 or 1> - Super jumps
cheat_bump_possession <0 or 1> - Possess touched character
cheat_bottomless_clip <0 or 1> - Toggle unlimited ammunition and no overheating for human weapons and plasma weapons
cheat_deathless_player <0 or 1> - Invincibility
cheat_spawn_warthog - Spawn Warthog
cheat_all_powerups - Spawn all power-ups
cheat_all_vehicles - Spawn all vehicles
cheat_all_weapons - Spawn all weapons
cheat_teleport_to_camera - Teleport player to current camera position
debug_camera_save - Save current camera location
debug_camera_load - Go to saved camera location, away from player
cls - Clear console window
quit - Quit game
Debug camera commands
Use one of the following commands to move the camera, after the "debug_camera_load" has been used.
A: Strafe left
D: Strafe right
Mouse Wheel Up or Down: Movement speed
Alternate ending sequence
Successfully complete the last level of the game in campaign mode under the legendary difficulty setting. The new ending features a human and alien fighting hand to hand. The human will say "Its over", and then they hug because they know the explosion will kill them both. Also, the FMV sequence of each battle scene will be slightly longer.
Multi-player mode catapult
For this one You have to be on a level that supports vehicles. The following weapons are requred: a plasma grenade, fragmentation grenade, and a rocket in a rocket launcher. When first trying this, back a Warthog up to a wall. Get on top of the Warthog's gun (not manning it). Look at the ground in front of the Warthog. Throw the plasma grenade in front of the Warthog. Immediately throw the fragmentation grenade directly on the plasma grenade. Then, immediately shoot the two grenades with the rocket launcher. You may be hurt in the process. However, you will be propelled high into the air if done correctly. This trick can be used to get on top of the cliffs in Blood Gulch.
Multi-player mode suicide
There are several ways to commit suicide in multi-player mode. Go to a level that has ceilings, preferably Rat Race. Get a plasma grenade, aim straight up, and throw it. Do not move. It will fall and stick to you, eventually blowing up and killing you. Another way is to have two plasma grenades. Throw the first one about ten feet from you then immediately throw another one about a foot in front of the other. Line yourself up with them. The second plasma grenade will be blown into you. Another way is to make a game play option where there are no shields and all shotguns. Go to a level with stationary Covenant shields. Get as close to one as you can with a shotgun. Shoot the shield and you will die.
Unlock New End Movie
Beat the game on the Legendary setting to unlock a longer, different final movie.
Alternate ending sequence
When You successfully complete the last level of the game in campaign mode under the legendary difficulty setting. The new ending features a human and alien fighting hand to hand. The human will say "Its over", and then they hug because they know the explosion will kill them both.
When the Grunts are sleeping you can beat them to death with the butt of your gun without waking up any of the other Grunts. You can usually kill a four to seven of them before an alien spots you. They start sleeping in level 5, Assault on the Control Room. Just remember not to shoot or they will wake up.
Use a photon weapon to destroy a Jackel's shield quickly. When you encounter a Jackel, run up and hit it with your weapon or get out a gun that uses bullets, not energy.
In the later levels of the game you will encounter new enemies called Flugs. These enemies will be small at first, but they will attack and control anything alive. Use a shotgun on these baby Flug as they tend to group in large numbers. By using the shotgun it will send a storm of bullets and kill most of them that are around. Use a shotgun on the possessed Flug, and it will kill most of them in one shot.
When Covenant dropship is getting ready to unload a group of Covenants, throw a grenade into the door as it opens. The blast will kill several of the enemies since they are all in one area.
Unlock New Guns
To unlock two new guns, You have to first beat the game on the easiest setting (Easy), and then on the hardest setting (Legendary) in under 3 hours.
Through one plasma grenade in a wide open spot, then stick another directly on top of it if you do this fast enough the first gernade will launch the second and vuaola fireworks.
Change of Seat
When one of your computer controlled buddies is in a vehicle spot/seat you want simply go over to that spot and press X.
To get infinite grenades, scorpion, and ghost in multiplayer- Go to the multiplayer screen: go to edit game types: In that menu you will have the option to make up your own game type.
If your going to use a plasma grenade, try throwing the grenade on the alien where it sticks onto them. It will blow up on them making sure it will kill the alien. Keep in mind the aliens can do this to you if you don't move.
Name in Blood
In the very last level of the game, as you're driving the Warthog out of the Pillar of Autumn, on the second jump, do not go all the way across. Then back into the room thats behind you and get out. if you look on the wall the name REX will be in blood on the wall.
In the very last level of the game, as you're driving the Warthog out of the Pillar of Autumn, get out at the 2 tunnel off of the main one and there will be a grunt at the end of it. he should say something like " I can't wait to get back to the ship and eat some grub!"
Elite Kill Trick
In the levels where you must face the Covenant there are certain aliens called Elites. They are the big ones which are usually blue, red, or sometimes yellow. If you have a gun with a scope ie; pistol or sniper rifle,try to get behind an elite without being seen by it. Next, Zoom in at the back of it, you will see yellow spots on his back or his head. If you shoot them a yellow liquid sprays out and they die instantly. This cheat helps because you only need to use 1 bullet and you do not have to get in close to kill it. It also looks cool when the yellow stuff sprays out.
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.
Extra shotgun ammunition
Take a shotgun that has 12 shots and 0 clips. After you shoot it a few times, you should be able to reload manually. You can do this about ten to twenty times.
Faster Warthog weapon use
This trick works best in multi-player mode. Drive the warthog in a straight line. When you see an enemy, jump out of the Warthog. Tap X repeatedly and sidestep to the right. If you are quick enough, you will exit the Warthog and jump on the LAAG gun without stopping, while the Warthog slows down. This also works well on ice, because you keep sliding.