Unlockables
Super-Marines - Kill Captain Keyes on "The Pillar of Autumn"
Unlock Second Ending - Beat the final level on Legendary

"Hidden Music" easter egg
Near the end of the 5th level (Assault on the Control Room), snag a Banshee in the open area and head up to the Control Center. There are three ledges that bracket the central pillar in front of the door; you want the middle one. You can land your Banshee parallel to the walkway, facing the left (with respect to the door), and hop out the back. Be careful - if you're not perfectly straight, you'll hop out to your death. Walk to the right end of the ledge... and stand still. You should hear this soft, sorrowful music playing.

Cheat
Go to the Settings Screen and press Y to make a new profile named '.fortune', and a strange message appears.

Easter Egg: Talking Grunt
WARNING: You may need to restart this stage if you pursue this easter egg.
In the last level of Halo, you'll arrive at a second grouping of tunnels after the dropship pick up goes awry. Take the first tunnel on your right and there should be a fork leading to a dead-end half way through. If you head partly that way, you can hear a grunt talking about something phenomenonally droll.

Hidden Area
In the chapter where you must find Capt. Keyes in the swamp, there is a secret area you can access right from the beginning. When Foe Hammer says ''The Last transmission from the captain's dropship was from this area. That was over twelve hours ago'', immediately start pressing your grenade throw button. whatever you do, DON'T MOVE! After a few seconds, the dropship will take back off, and you'll still be in it! It flys for about 20 seconds then crashes. Press ''X'' to exit the dropship. Now walk directly away from the ship until you reach a clearing. Head towards the center and out of the fog you'll see a lone Marine standing there! He won't move or say anything, unless you shoot him in the foot w/ your pistol.

The Megg
The story behind the Megg is a long one so I'll just give the steps to accomplish it:

1.Select Campaign and play Pillar of Autumn on Legendary
2.Once you're out of the cryotube, turn around and hop on top of it
3.Jump off to your right on top of the shield generator
4.Hop on the above grated walkway and turn right
5.Run to the wall above the doorway and touch it
6.Turn around and run and touch the wall on the other side of the walkway
7.Then jump to left on top of the yellow-striped barrel
8.Jump back on the walkway, run back and touch the wall above the doorway
9.Walk off to the right and go through the door

Continue through the level as normal, until you reach the marine that tells you to follow him. Make sure you jump over him and make him follow you. Once you reach the bridge, dodge Captain Keyes, and the cut scene, and fall into the glass pit behind the space grid. Go up the ladder, but make sure the caption appears, the one that tells you how to go up ladders. Now go talk to Captain Keyes.

10.Get your assault rifle from the cafeteria door
11.Reload the rifle and turn around and run back the bridge
12.Shoot Captain Keyes, melee him or melee one of the standing crewmen. Cortana will order the invincible marines
13. Run to the door from which they come on the right (shoot them as you go so they don't come charging) and through the door behind them

Run through (the marines shouldn't follow you any further) and walk into the end room. Look up at the end of the secret room and you should see a bloody love heart with a 'M' shot onto the ceiling.

The Rex
While playing the level ''the maw'', when you rach the part where the ship crashes, keep going until cortana tells you about the big jump, then try to turn a bit and land on the side wall. if done right, you should be able to access a room the has blood stains all over. if you look carfully enough, you can find the word REX on the wall written in blood.

Attack On The Control Room Glitch
When you are going back through the Attack On The Control Room stage, your objective is to destroy all the generators. The moment you or your partner gets close to the last generator, the flood will kill you. Instead, exploit the co-op system to your advantage. Notice that on co-op, when one of you is further ahead then the other player, the lagging player is warped ahead. At the hallway before the last generator, spend a moment and practice finding the warp spot, now when you're sure you've located this spot have one player stand a step away from the spot that will cause the other player to warp. Have the player that will warp go deactivate the last generator. Now as soon as the surge occurs, have the player in the hallway cause the warp and both players can leave relatively unscathed.

How to get a banshee into a cutscene
:CO-OP only:On the level assault on the control room,at the last open area,when you come out onto a bridge and there are some grunts, some elites and two banshees; run really quickly to one of them while your parner kills the covent. Get in and fly to the really big door that is the beginning of the last part of the mission. Your partner can kill himself and respawn there for the sake of speed.Open the door and kill all the covenant untill you get to the last door(the one before the final cutscene of that level). While one person opens the door the other should fly at it with the banshee (this takes timing, get a save point before you try it), and start from there again if you mess up. If done correctly the banshee will be in the cutscene as it starts. If you are really lucky then the banshee may run over MC during the cutscene!

No Enemies At Assault On The Control Room
*Only on co-op mode*
On the first bridge, have one person go to the lower floor. Jump off onto the wall/cliff and land on the side. Then have the other person die. Wait for the other person to get teleported. Bring the second person to the lowest part of the cliff and make sure he can die in one punch. Have the first person run to him and hit him while moving and then jump off of the cliff, staying by the wall. You will be moving to fast for the other person to be respawned. But if you do it right, you will hit a cliff lower than the one you were at, and for less than a second, you will be alive (although you arent able to notice by watching you fall). At that time, if you did it right, the second person should be respawned at the lower cliff. Then wait for the first person to respawn. Go to the lowest spot on that cliff by the trees where the marines are (at the lower level). At the lowest spot at the cliff, fall down. make sure you stay by the wall. This may take a few tries, but if you do it correctly, you will be alive, probably with no shield and one life bar left. Then go to the door, and get the checkpoint. At that point, there will be no enemies, marines guns, or ammo. But there will be blood (where there would be ammo from dead marines) and transportation. There will be no more enemies for the rest of the level.
*This glitch is extremely hard to pull off at the cliff jumping.*

Three guns on the first level
Towards the beginning of the game, there is a way to bypass the two weapon limit and carry three weapons at once. On the first level, make your way to the bridge. After speaking with the captain, quickly run out of the bridge before the chapter name disappears. If you were fast enough, the checkpoint at the door will not trigger. Now run to the mess hall and get your Assault Rifle and another weapon. Now, run back to the bridge and trigger the checkpoint. When you go back towards the mess hall, the pistol will appear in your hands, and you will be carrying three weapons instead of two. Each gun reloads and exchanges normally. Note: This only lasts for the first level.

Top of Silent Cartographer
There are a few way to reach this area:
-Get a Warthog and do the Warthog jumping trick with an overshield to fly yourself over on top of the island.
-Get a Warthog through the tree barrier and park it to the left of the last big rock up the small hill. Then, pick up a overshield and go back to the Warthog. Get on top of the Warthog and throw a plasma grendade on the Warthog. Wait 2 seconds and jump. The blast should throw you up onto the top of Silent Cartographer.
-Go past the tree barrier to the Hunters. Kill 1 and pick up the overshield. Make the remaining Hunter fallow you to the big rock where the last trick was performed. When the hunter slashes you on the second slash you will go up. Jump at this time and the Hunter will hit you up onto the top of Silent Cartographer.
-Go past the tree barrier, kill all enemies and Hunters, and pick up the overshield. Get a fragmentation grendade and jump on top of the rock, where the last 2 tricks were performed. throw the grenade straight down and time it so the blast will throw you on top of the Silent Cartographer.
-In Co-op get a Warthog through the tree barrier and make your partner get into the gunner. Park the Warthog where you did in trick 2 and aim the gunner to the smallest part of the ledge. Make the driver get out and jump on the gunner's gun. Run and jump off the gunner and you should be able to reach the top of Silent Cartographer.

Unlimited Camo Trick
Select the Assault on the Control Room level on any difficulty in Co-Op mode. Next, skip to the part where there are two tanks, and a banshee flying over you just before a cave. You'll notice a cloak to the right of the tunnel next to some ammo. Keep Player 1 by the cloak, and have Player 2 beat the entire part just before you trigger the Rolling Thunder loading zone after the bridges. Now have Player 1 actually go cloaked and at that point Player 2 should walk through and trigger the Rolling Thunder loading zone. Player 1 will be spawned all the way down by Player 2 and for the rest of the level be cloaked without it ever wearing off. The only way it will wear off is if Player 1 (not 2) dies.

Unlimited Rockets
Select the Assault on the Control Room level on any difficulty in Co-Op mode. Next, skip to the Rolling Thunder loading zone after the bridges part. Have Player 1 fire a rocket in any direction. Now, at the same exact time, Player 1 should reload the rocket launcher and Player 2 should walk through the loading zone. Player 1 will now have unlimited rockets until the end of the level. This trick will wear if it Player 1 dies, reloads, or switches weapons.

Weapon Switch
You need two controllers for this. Choose Campaign, select any level on any difficulty. Using either controller, choose what weapon you want to change. Remember what weapon you chose. Now cross a checkpoint. Save and Quit, and grab the other controller. Use the same profile you used and go back in that level. Now get a different weapon. After you do, cross another checkpoint. Save and Quit. Use the first controller you used in the beginning. Chose the same profile and level. The second weapon now has the same skin as the first weapon. It still has the same characteristics. Example: you changed the skin of a Rocket Launcher to an Assult Rifle, but it won't shoot as fast as a Assult Rifle does.

Weird Ending
At the ending of Assault on the Control Room before going straight to the controll for the cutscene, after opening the doors use the ghost to go through the control room by first opening the door to the control room and get back to the ghost and ride through the cutscene, the Master Chief will get run over by the ghost and you'll see a weird ending with the Master Cheif stuck on the ground but still talking with Cortana. This glitch works with single or co-op, just that one of the player have to use the ghost through the cutscene.