Halo: Combat Evolved/Secrets

Different Ending
To get a different and longer ending movie Halo, beat the final level on Legendary.

Hidden Music
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. Just so you know, the name of this masterpiece is called The Siege of Madrigal, and it can be found in Bungie's earlier game, Myth. It was written by Marty O'Donnell from Total Audio.

Talking Grunt
Note: 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 Captain 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 flies 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.
 * 10) 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.
 * 11) Get your assault rifle from the cafeteria door,
 * 12) Reload the rifle and turn around and run back the bridge,
 * 13) Shoot Captain Keyes, melee him or melee one of the standing crewmen. Cortana will order the invincible marines,
 * 14) 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.
 * 15) 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 reach 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 that has blood stains all over. If you look carefully enough, you can find the word "REX" on the wall written in blood.

Double Punch
While in gameplay, press the melee button (hit), then quickly throw a grenade, then quickly melee again. The entire process should take one about 1.5 seconds to do this.

Marines Hate You
On any Campaign Mode level, (co-op or single player) just start attacking the Marines. Sooner or later, they will start to fight back, and when you target them the crosshair will be red.

Skip Part of Silent Cartographer
When you unlock the door to the cartographer place, You will fight invisible elites. After that, go outside, look right and you will see some overshields. Get one and jump from the ledge towards the downed pelican(With rockets) you will fall, lose your overshield, but not get hurt. there will also be a warthog to hop in.