Press/hold down on the d-pad, RS, reload and switch grenade.

In Mission 7, you can change the music to the tracks "Never Surrender" and "Siege of Madrigal" in Club Errera. During Mission 7, once you get to the Club Errera part of the mission, head back to the hospital. Fly to a ledge below the usual entrance. If you chose the right one, when you get out you should see a green light. Once found, activate it and go back to Club Errera. Land and when you walk in the song "Never Surrender" will be playing. If you want to change the music again, go back to your Falcon and fly to the roof of Club Errera. Guess what, there's another switch. Activate it and the song "Siege of Madrigal" will now be playing. If you return to the dance club after you clear it out (Hunters included) then a Brute DJ will be spinning records, a Brute tends the bar and Grunts get freaky.

Upon completing the final level (The Pillar of Autumn), you will see a cut-scene of the ship taking off. When the cut-scene starts, hold your aiming stick (it will be dependent on your control scheme) so that you would "turn right" normally. At the point when the UNSC shuttle docks at the Pillar of Autumn's landing bay, the camera will move to the right (if you were holding the stick to aim right) and catch a shot of a Spartan in a capsule. Should look familiar, right?

Clear a Campaign mission on Legendary without dying.

Earned a Bulltrue medal in either multiplayer or Firefight Matchmaking.

Earn a Killtacular in multiplayer

Kill 100 enemies in a row without dying in either the Campaign or Firefight.

Avenged a teammate's death in multiplayer Matchmaking

A Monument To All Your Sins (150) Completed every mission in Halo: Reach alone, on Legendary.
A New Challenger (10) Completed all of the Daily Challenges in a given day.
A Spoonful Of Blamite (10) Killed 10 enemies in Firefight or Campaign with a supercombine explosion.
A Storage Solution (5) Used the File Browser to upload a file to your File Share.
An Elegant Weapon (10) Killed 10 enemies in a Firefight or Campaign session with the DMR.
An Honor Serving (25) Reached the rank of Captain in the UNSC.
Banshees, Fast And Low (25) Hijacked a Banshee during the Reach Campaign.
Be My Wingman Anytime (5) Let a teammate spawn on you 5 times in an Invasion Matchmaking game.
Blaze Of Glory (25) Scored 200,000 points in a Firefight game.
Cool File, Bro (5) Recommended a file to someone.
Crowd Control (10) Earned a Killionaire medal in Firefight.
Doctor, Doctor (5) Used a Health Pack to replenish life after taking body damage.
Dust And Echoes (10) Completed the 8th mission on Normal or harder.
Firestarter (10) Scored 50,000 points in a Firefight game.
Folks Need Heroes... (50) Completed the Campaign on Heroic difficulty.
Game, Set, Match (25) Completed a Firefight set on Legendary without dying.
Gods Must Be Strong (125) Completed the Campaign on Legendary difficulty.
Heat In The Pipe (75) Scored 1,000,000 points in a Firefight game.
I Didn't Train To Be A Pilot (10) Killed 3 of the anti-aircraft batteries during the 8th mission.
I Need A Weapon (10) Completed the 4th mission on Normal or harder.
I See You Favour A .45 (10) Killed 10 enemies in a Firefight or Campaign session with the M6G pistol.
If They Came To Hear Me Beg (25) Performed an Assassination against an Elite to survive a fall that would've been fatal.
Into The Howling Dark (10) Completed the 7th mission on Normal or harder.
KEEP IT CLEAN (5) Killed 7 Moa during the 2nd mission of the Campaign.
Knife To A Gun Fight (5) As an Elite, killed 5 Spartan players in Matchmaking.
Lemme Upgrade Ya (10) Advanced a Commendation to a Silver state.
Lucky Me (25) Earned a Triple Kill while Jetpacking in Campaign, Firefight or Matchmaking.
Make It Drizzle (10) Purchased an item from the Armory.
Make It Rain (10) Purchased an item from the Armory that required the rank of Lt. Colonel.
One Down, 51 To Go (10) Completed a Weekly Challenge.
Protocol Dictates Action (10) Completed the 3rd mission on Normal or harder.
Score Attack (10) Scored 15,000 points in Score Attack Firefight Matchmaking.
Send Me Out... With A Bang (10) Completed the 10th mission on Normal or harder.
Skunked (10) Won a game of Invasion in the 1st phase.
Swap Meet (10) Traded weapons with an AI ally in Campaign.
Tank Beats Everything (25) Finished the 9th mission on Legendary with the Scorpion intact.
That's A Knife (10) Performed an Assassination on an enemy.
The Soldier We Need You To Be (25) Completed the Campaign on Normal difficulty.
The Start Of Something (15) Reached the rank of Corporal in the UNSC.
They've Always Been Faster (25) Cleared the 2nd mission without setting foot in a drivable vehicle.
This Is Not Your Grave (10) Completed the 9th mission on Normal or harder.
To War (10) Completed the 5th mission on Normal or harder.
Two Corpses In One Grave (25) Killed 2 vehicles at once with the Target Locator in the 3rd mission.
Wake Up Buttercup (25) Destroyed the Corvette's engines & escort in under 3 minutes in the 6th mission on Heroic or harder.
We're Just Getting Started (10) Completed the 2nd mission on Normal or harder.
What's A Killing Spree? (5) Earned a Killing Spree in multiplayer Matchmaking.
Yes, Sensei (10) Earned a First Strike Medal in a Matchmaking game.
You Flew Pretty Good (10) Completed the 6th mission on Normal or harder.
Your Heresy Will Stay Your Feet (25) Killed the Elite Zealot before he escaped during the 5th mission.