NOTE: Reading this walkthru will not get you through Legendary, it is done for Easy mode only. Also, I'm assuming at this part, that you have a Rocket Laucher (with 10 rockets) as one of your weapons.

Now to the walkthrough.

After defeating (or fleeing) the two Hunters in the room, you will get through a corridor and soon reach a door. At this point the "If I had a super weapon" part begins. Now, DON'T go through the door, now I'll tell you how to get a Banshee earlier than usual.

Pull out your Rocket Launcher and get ready to use the zoom. Then, strafe to the left of the door (facing the door and along the wall to the left). Next, approach the door until it opens. The moment the door has opened, quickly zoom in and shoot the Elite in the background (the one nearest the Banshee). If done correctly the Elite should die and the Banshee will stay there.

Make quick work of the second Elite as he could steal back the Banshee. Then, make your way towards the Banshee while shooting the scrambling Grunts. Defend the Banshee until there are no more enemies nearby.

While you were busy shooting up the group of Grunts, another Elite took off in a Banshee and is now shooting you. Pull out your Rocket Launcher and shoot down the Banshee (don't take off and start a dogfight, you might lose too much vehicle health).

-If you couldn't get the Banshee, scroll to the bottom of this text. Otherwise, carry on reading.-

Now that the enemy Banshee is out of the way, take off in the captured Banshee and make your way to the top of the Pyramid. Land close to the door control and open the doors. Now, if the Banshee is still pretty fit, take off and shoot a Fuel rocket (right mouse button) at the yellow Elite with the large, blue sword before he jumps on top of the vehicle. Make quick work of the Grunts and fly in the long corridor. At the end of it, two Elites are waiting. Get rid of them and land your Banshee.

Activate the last door opening and fly to the very last door (the one that triggers the scenery) and land. Open the door and watch the movie, you then move on to "343 Guilty Spark".

-If you didn't get the Banshee, read this.-

If you didn't get the Banshee, proceed all the way across the bridge and kill any enemies. Make you way into the structure and kill (or evade) any enemy inside. Find your way to the elevator which will take you down to the ground floor. Again, eliminate any threat on this floor (or evade them again) and make your way outside.

You should see a patrolling Elite and a Ghost. Cortana will hint you to commandeer the Ghost as you'll need the firepower. Try to sneak up on the Elite and kill it. Get the Ghost and make your way up the Pyramid. Kill any enemies along your climb and replenish yourself with ammo along the way.

Once you get to the top, you should be facing 3 Shades (empty, phew!). Soon, a Grunt comes down and attacks you. He is soon followed by another and, UH-OH! Two Hunters rush down towards you. Pull out your Rocket Launcher (right now I'm praying you still have ammo for it) and get rid of them ASAP.

Then, make your way up the slope to the door's control panel and open the door. Now, don't wait there and think you've passed the level. Run and duck behind one of the energy shields facing the door. Once your behind it, you will be 'invisible' to any Covenants. Take the time to spot and aim at the yellow Elite with the huge sword. Then, you can either toss a grenade so it sticks to it (and kills it) or shoot it with whatever you've got (basically, get rid of him FIRST).

Once you get rid of the Elite, take out the Grunts, replenish your ammo/battery life or grenades and make your way to the end of that corridor. You should bump against two Elites, get rid of them and then open the door. Make your way through the last stretch (no enemies here, as Cortana says) up to the very last door (the one that triggers the scenery).

Congratulations! You've finished the level, the scenery starts and then you embark on the next mission: 343 Guilty Spark.

Hope this helps.