all about the cheat game

Cheat mode (Custom Edition):
Start the game with the -console -devmode command line parameter. Press ~ during game play to display the console window, then enter one of the following codes to activate the corresponding cheat function. Note: 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.
Effect Code
Toggle instant deaths for enemies that see player cheat_medusa <0 or 1>
Set game speed game_speed <0-20>
Clear console window cls
Toggle unlimited ammunition and no overheating for human weapons and plasma weapons cheat_bottomless_clip <0 or 1>
Unlimited ammunition cheat_infinite_ammo <0 or 1>
Super jumps cheat_super_jump <0 or 1>
Possess touched character cheat_bump_possession <0 or 1>
Invincibility cheat_deathless_player <0 or 1>
Spawn Warthog cheat_spawn_warthog
Spawn all power-ups cheat_all_powerups
Spawn all vehicles cheat_all_vehicles
Spawn all weapons cheat_all_weapons
Teleport player to current camera position cheat_teleport_to_camera
Save current camera location debug_camera_save
Go to saved camera location, away from player debug_camera_load
Quit game quit

Debug camera commands:
Use one of the following commands to move the camera, after the debug_camera_load has been used.

W: Forward
S: Back
A: Strafe left
D: Strafe right
R: Up
F: down
Mouse: Turn
Mouse Wheel Up or Down: Movement speed

Screenshots:
Start the game with the -screenshot command line parameter. Press [Prt Scn] during game play to copy the current screen to the clipboard. You may now paste it into the program of your choice.

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.

Alternate dialogue:
Playing under the legendary difficulty setting introduces new dialogue not heard in other modes. For example, after being massacred by a force of Grunts, Jackals and Elites, one of the grunts asks, "Can I have his helmet?". Also, your fellow Marines seem to be a bit more chatty (as well as profane).

Under the legendary difficulty setting, view the entire first FMV sequence. During the sequence, the General says things very differently when compared to the sequence under the easy difficulty setting.

Hint: Haloball: Get Warthog out of stadium:
There are two ways to do this. One is to place a Warthog in a corner, with the front facing out. Use it as a ramp for other Warthogs. The other method is to place a Warthog in a corner, then throw a plasma grenade under it, followed by a fragment grenade. When it flies up, shoot it with a rocket to knock it up to the stands. Note: Sometimes the Warthog slides off. Another rocket can knock it up farther and, sometimes prevent it from falling off.

Hint: LightningStrike: Banshee:
Get a Ghost at one of the bases and drive up onto the mountain. Once on it, find a way to get to the other side of the map. You will find a Banshee over there.

Hint: LightningStrike2: Secret room:
Go to the Red base and walk into the corner where there is a group of rocks. You will go through a secret teleporter find yourself under the bridge. Once there, look around for a trench. Get in it, and look for a small corner with a shotgun in it. Walk into that corner and you will find the secret room. There are rocket launchers, snipers, active camo, grenades, and overshields, along with a few pictures and a list of the beta testers.

Hint: SaberArena: Get on top of billboard:
To get on top of the billboard advertising a Warthog, face it and walk into the left corner of the map. You will teleport up to it. You will find a laser rifle. The only way off is to jump.

Hint: Streets Of Earth City: Nuclear signs:
There are two signs in the map that will kill everyone nearby if they are shot. One is on the central tower, and the other is in the place where you find the Lifepod.

Hint: Streets Of Earth City: Find Lifepod:
There are two ways to find the Lifepod. One is to fly around under the map until you find the place in one of the pillars. Another is to use a teleporter on the side of one of the towers. Note: To use the teleporter, you must use a Banshee and get out while directly in front of the teleporter.

Hint: Multi-player mode suicide:
There are several ways to commit suicide on 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.

Hint: Multi-player mode catapult:
Go to 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. Note: You can use this trick to get on top of the cliffs in Blood Gulch.

Hint: Disappear from enemy radar (demo version):
Crouch when you walk. It is a very slow technique, but it works. It is very useful if you grab active camouflage (in the middle of the Blood Gulch map) and do the crouch technique. You will be practically invisible to any enemy radar or eyes.

Glitch: Shoot enemy through wall:
In multi-player mode, drive any Warthog close to a building so that the side of it is touching. Get in the gunners turret and turn it towards the wall. If done correctly and you are close enough, you should be able to to shoot at an enemy through the wall and not receive damage from them if they shoot back.

Glitch: Go to moon in Streets Of Earth City:
Get a Banshee, Pelican, or Lifepod and fly up to the central tower. Once there, freefall to the bottom of the map, which you will go through. If you do not freefall, you will not go through. If you do not get it the first time, try it again. Once out, fly toward the moon. You can also fly to the big red planet with this glitch. The moon is about twenty minutes away. Note: When out, do not fly straight at the moon or you might enter the map again.

Glitch: Sniping location in Blood Gulch (demo version):
Get in a Banshee. Fly to the rock with the circle in it. At the side facing the Red base, back up into it. The tail should be facing it and physically in contact with it. Jump out and you will be on the rock. You can now snipe from there.

Glitch: Enter rock in Blood Gulch (demo version):
Get in a Warthog. Drive to the pointy rock near the middle the map. Back up into it. The bumper should crash into it. Get into the gunner's seat and jump out. If done correctly, you should be inside the rock. You snipe people from inside. Bullets cannot effect you, but plasma weapons, explosives, and flamethrowers can.