The Pillar of Autumn/Walkthrough
From Halopedia, the Halo wiki
This is a walkthrough for the ninth level of Halo: Reach, The Pillar of Autumn. It is written for play at the Legendary and Heroic difficulty.. You're accompanied by Emile-A239 and initial loadout is an MA37 Assault Rifle and M6G Pistol.
Once More Unto the Breach (Mission Start)
The Abandoned Bridge
The first encounter is a tough one. You have three Grunts with an Elite Major (or Minor) on the left, three more Grunts with an Elite Ultra on the right, three Jackals guarding the bridge, and three Grunt Heavies underneath it. Although the enemies are unaware of your presence when you arrive, they're so closely gathered that trying to take them out by stealth is impossible. Cover is also very limited here, as most of the rocks are too short to hide at and make you a target for grenades. While you have more than enough assault rifle ammo, your pistol only has 24 rounds, half of its total capacity. So you're going to have to make do other weapons while saving your pistol for the absolutely necessary.
First priority is the Elite Major and his Grunts, who are patrolling by a dilapidated flatbed truck. Head to the left, aim for the Grunts and toss a grenades; you should get one or two. The rest you target with your assault rifle, short controlled bursts. When they're dead, the Elite Major will retreat to hide at the truck's front, so head for the back of the truck for cover. Although he'll fire some harassing shots, he won't charge your location. When the three Grunts are dead, Emile will start coming down the mountain, and so the enemies will focus of him. Look past the truck to the bridge and you'll see the three Jackals shooting at him. They'll be oriented such that you can headshot one with your pistol. Once one of the Jackals is dead, the others will retreat up the bridge, and now you'll have a lot more room to move. Emile will now try to regroup with you, and in the process charge at the Elite Major. Sometimes he'll even kill it, but not always, so take it out with melees or assault rifle while it's distracted and injured.
Now every enemy in the area is aware of you, but they'll mostly harass from a distance. Your next target is the Elite Ultra, but he's guarded by the six remaining Grunts and the Jackals. He also have a concussion rifle, so trying to rush him is foolhardy. So focus on reducing his guards. Target either of the Grunts. For the Minors and Majors on the right side of the bridge valley, use your assault rifle, as you have plenty of rocks to fire from cover. For the Heavies on the left, use your pistol, as there's less cover on the left and they have better aim. As for the Jackals, stay off the bridge until the Grunts are dead; engage them too early and the Ultra will start blasting you. When he's fallen back because his Grunts are dead, then you can take the bridge. Rather than using your limited pistol shots or one remaining grenade to get them, try the dead Major's plasma rifle. Using the truck on the bridge as cover, orient yourself so you can see their shield but they can't shoot back at you. Then tear through their shield with plasma shots.
The Ultra is the last target, and he's fallen back to the cliff on the left across the bridge. With plenty of plasma pistols and hopefully saved magnum ammo, you should be able to noob combo him while he's distracted by Emile.
The Mongoose Drive
The drive down the road with the Mongoose is a brief section that doesn't warrant much strategy. Just keep moving, drift your turns, and don't let Emile drive. But before you drive along, you may want to arm up for a secret encounter. At the small supply house where the Mongooses are parked, there's a dead Marine with a rocket launcher. Inside there's more rocket launcher ammo. In total there are twelve rockets, and four Banshees spawn as soon as the music changes. With four rockets to spare, why waste them?
Grab the rocket launcher and look to the right in the sky, just above the cliff that the road passes through. You'll see four Banshees coming in, three in V-formation, one a little off to their right a bit faster. Target them with the rocket launcher's lock-on to blow them up. Their AI increases the closer they get to you, so the first two usually connect while the next two Banshees get more evasive. If one attacks you, use that chance to fire straight into it; they typically just use their plasma shots and not their fuel rods. If they dodge the rockets, wait for a bit, as the rockets typically circle around for a second try. With only four extra rockets, don't use anymore, grab a DMR as well before you leave, then drive along.
Only last thing you need to know for the Mongoose drive is that a Phantom flies over after you pass through a tunnel and then it comes over the broken bridge you have to jump. Since it shoots at you with its turrets, avoid it on high difficulties by stopping for a bit and letting it drive past.
The Brute Blockade
Across the bridge, the Covenant have barricaded the road. Guarding its end are ten or so Brutes, a few Grunts and Jackals, two Jackal marksmen in a lookout tower, and worst of all, a Wraith at the very end of the road. After them come three more marksmen in the rocks past, and four Grunts that like to go kamikaze.
The typical way of this section is safe but tedious. Since you have a hill to shoot from and lots of DMR ammo in the neighboring house, it's easy enough to just pick off all the infantry one by one until it's safe to challenge the Wraith. You're so far away that the Brutes cannot shoot you, but there's so much cover in the area that the battle becomes a long game of waiting for them to exit cover. More risky close-combat doesn't pay off because of the Wraith. Its aim is great with its mortar, and trying to go for the Jackals' needle rifles in the lookout will just have the Wraith blast you out of the air. It will also dodge your rockets if you try to bomb it from long-range. So if you want to do this safely, just stay back on the right of the house and slowly headshot everything.
But if you want a much faster and more creative way of clearing this area, then you have to do things a little out of order. The plan is to engage the marksmen-kamikaze group first, so that you can grab their weapons and use them to hijack the Wraith, followed by blasting everything. Done right, the entire Brute pack can be shelled in just two minutes after arrival. Here's how.
After you jump over the broken bridge, leap off your Mongoose and cross the road barrier to head to the small cliff on the left. Across it is a weapons house, a garage, and a stone hill that run parallel to the valley full of the Brutes and the Wraith at the end. Get to the left corner of the small cliff and use a Sprint jump to get on the roof of the weapons house. It takes a while of practice, but try to aim for the roof's corner, than the top, then jump up the "steps" to get on top. If you miss, revert the checkpoint or even just run back up to the top. The enemies will be focusing on Emile, and if any Brutes corner you then stick them with a plasma grenade. Once you get on the roof, head along the top and jump on the garage, then at its end sprint jump onto the top of the hill. The Wraith will see you by this point, so keep moving. It's also possible to get on top of the hill by running through the garage and then sprinting up it, but there may be enemies inside it and they're not going to let you just past them by. Once you're over the hill, the Grunts will charge with grenades and the Jackals will shoot. Use your DMR to target the Grunts first, then the Jackals. Done fast, and you might blow up the entire group.
Now you're behind the hill and have plenty of cover to steal the Wraith. Trade your weapons for a needle rifle and a plasma pistol. Then look for the Wraith and take out its gunner. The gunner is always a Brute Captain and he can't be supercombined with the needles if he's in the gunner seat. So shoot him five times in the head to kill him, then close the distance with the Wraith with a plasma pistol overcharge. When you do, Emile will charge through all the Brutes to get to you, so he'll somewhat distract it. Jump on top of the Wraith, switch to your needle rifle, then jump in and out of the gunner seat to force out the driver. Once you're both out, supercombine or sticky grenade him, then jump into the Wraith and bomb everything.
Your only worry is grenades, so keep strafing to dodge them. Sadly you can't bring the Wraith with you to the rest of the level, so arm up once everything is dead. Pick up any needle rifle ammo from the dead marksmen around the area and also pick up your rocket launcher that you left. Then follow the waypoint to the caves.
The Drone Caves
The Yanme'e in the caves are annoying, but there are less of them than it feels like there are. In the first room, there's ten. Use your needle rifle to shoot them; even if you miss a headshot, three bodyshots will kill them. Don't worry about conserving your ammo; there will be more than enough needle rifle ammo in the next area and there's full DMR ammo by the entrance if you need that instead. Also, try to shoot the Drones unscoped, so that their shots don't constantly pull you out of scope. As their numbers diminish, they'll retreat further back in the cave.
The next room has five or so Drones, and Skirmisher Majors and Murmillos with needle rifles below them. Focus on the Drones first, as they're the more mobile threat. The three Skirmishers Majors can be picked off from above with a headshot each, and the Murmillos will hang back. Before dropping down after most of them are dead, go back for the DMR and drop-carry it to come down with you; you'll need it for the next area. Then keep your distance and headshot the Murmillos. You're likely low on needle rifle ammo, but you'll find tons from the dead Skirmishers to completely refill it. When you hear the music reach a long low note, that means the area's been cleared. Move on ahead with a needle rifle, a DMR, and your rocket launcher.
This Town Isn't Big Enough (Rally Point Alpha)
The Boneyard (Starboard)
The Boneyard is the largest battlespace in the level, and there are tons of ways to complete it. But the safest and most efficient way to use what you have available at the cliff to you enter from before heading down. At the cave exit you'll have a grenade launcher, a Spartan Laser, frag grenades, and an Armor Ability case carrying both Armor Lock and Drop Shield. And of course you have your weapons from before, needle rifle, DMR, and rocket launcher.
Despite your safety from on high, you actually do need to hurry as you carry your weapons from the previous section. Below you are two fields separated by a wall. The left field has some troopers fighting a bunch of Jackals, some Skirmishers, and an Ultra Elite. The right field has some more troopers fighting some Jackals, Skirmishers, and an Elite General armed with a Fuel Rod Gun. Hanging back are an Elite Minor and Major, and two Ranger Elites really far back on the deck of the parked Commonwealth. Keeping the troopers alive is to your benefit. While they're around the enemies will focus on them than on you, but you need to hurry because they're not going to last long against this horde.
Your first priority is the General. He's too far away to kill you with his cannon, but surviving him isn't the hard part. Your first inclination might be to blast him out with the Spartan Laser. But the Laser has been nerfed since Halo 3. It only has four shots now, and each shot is roughly twice the strength of a sniper round. Since Generals and Ultras take three sniper shots on Heroic and four shots on Legendary to be killed, this means one laser won't be enough to kill him. Worse, his shields recharge in only four seconds, and it takes five seconds to charge a second shot. So if you try to take him out with only the Laser, he'll tank every shot. After taking one, he'll also be aware of your presence and dodge a lot, making aiming harder. The only way you'll kill him with just the laser is if the beam also hits the broken trucks some yards away and he's close enough that the combined laser+explosion kills him. So if you're going to hurry to kill him and save the troopers, here's what you do.
As soon as you hear a female trooper yell out "Spartan, over here!" and Emile has a dialogue with Captain Keyes, make a beeline for the weapons at the cave opening. Keep your DMR, and trade your rocket launcher for the Spartan Laser. Charge up a shot, aim for the General, and right after it strikes switch to your DMR and shoot his shields until it breaks and he's headshot. Now that he's dead, pick off all the Jackals and Skirmishers you can from this cliff with your DMR. No worries about ammo, since there's plenty more DMR ammo ahead. As for the Elites, use the Spartan Laser. With the Ultra, use the same strategy, laser and then DMR. The Major and Minor will hang by the trucks and can be blown up, and you should be able to laser at least one of the Rangers. Once your laser ammo is depleted, go back to grab the Drop Shield and your needle rifle and rockets.
Head to the right field where the General was; it's much more open than the left field and the cover is bigger. Be sure to drop-carry all three of your weapons down there too. Your priority is any Elites still alive, and this closer range the Noob Combo is the most effective. The remaining Ranger will move up now and he'll have a concussion rifle; all the other Elites should have plasma weapons. Use your DMR and any plasma pistol you can find before the Elites arrive, and deploy your Drop Shield if things get hairy. If you need bullets, there's a dropped DMR by the cover closest to the cliff. If there are any Skirmishers alive alive, let them come to you; they carry plasma pistols and can basically bring a fresh one to you should you need it. Don't use your needle rifle at all, but the rockets are utility. If you find yourself in an extreme emergency, the rockets are your "get out of jail card". You can use up to four to save yourself if you need to blow up a rampaging Elite immediately.
Once everything is dead, leave your DMR behind, take your needle rifle and rockets, and head for stairs leading to inside the Commonwealth.
The Boneyard (Port)
You're leaving behind your DMR because there's plenty more inside, and also because of a time-sensitive matter: a BOB. A Gold Ranger Elite may spawn at the other end of the next area and you want all the time you can to snipe him. He'll be on the far right by a Shade turret, and it will take three to four sniper shots to kill him.
The port side of the boneyard is mostly Grunts, a few Elites, two Ghosts, and three Shade turrets. Most of the enemies are too far away to seriously harm you, and you have plenty of long-range weapons with you at this balcony. There's a sniper rifle with twelve rounds, a Spartan Laser, another Spartan Laser on the ground floor, and a DMR crate to the left near the stairs. Plus you have your needle rifle and rockets. Set aside your needle rifle for now and use the rockets to destroy the Shades. While you could use the Spartan Lasers, you should save one of them for later and it's easier to fire-and-forget a rocket than to charge up the a laser and hope the Shade doesn't notice you for five seconds.
After the Shades are destroyed, the next priority threat is that Grunts with Fuel Rod Cannons. Headshot them with the DMR or sniper rifle. Feel free to use all the sniper ammo on all the other Grunts and Elites, and any remaining rockets can be used on the Ghosts. Emile will be on the ground floor distracting them, and sometimes he'll even hijack one. If they're still around and the rockets have missed, lure them close to you so you can use grenades or use one of the Spartan Lasers; save the ground floor one. Once everything is dead, drop down (the fall won't kill you, just cause some shield damage), cross the field, and bring along your DMR, needle rifle, and a Spartan Laser.
You have one more room on the opposite side before completing the boneyard: the generator room. Inside there will be two Ultra Elites, two minor Elites, and some Grunts. While you could possibly noob combo the Elites with a DMR and plasma pistol, there's a more explosive way of beating it. Before entering the building, leave your needle rifle and laser for your DMR, spare plasma grenades, and a Fuel Rod Gun from the dead Grunts. There should be enough ammo for three FRG clips. Then enter the building via the stairs on the outside left. This will take you to the second floor, where past the door you'll see an Ultra Elite standing by unaware. Stick him with a plasma and then blast him away with a fuel rod; you'll need both to kill him. The enemies inside will panic and the other Ultra will come up the stairs for you. As he reaches the top, stick and blast him too. If you screw up, fall back and Emile might distract him. The rest of the enemies will stay on the ground floor and thus can be easily bombed with the remaining fuel rods.
The Trapped Troopers and the Hunters
Before entering the next area, it's necessary to note a frequent glitch. When leaving the boneyard and going further into the next room, the game will load the next area and in the process de-load all the previous ones. If you're drop-carrying weapons, then sometimes it will despawn the weapon currently on the floor and leave you only with the two you're carrying. If you drop-carry them quickly enough, then most of the time you'll avoid this. But if it keeps happening, then your utmost necessary weapons are your needle rifle and Spartan Laser. There will be no DMR ammo in this section and the next, but there will be enough needle rifle in the room following those to replenish half capacity, plus more DMRs. Use your needles sparingly.
You'll pass through a hallway and office to reach a wide room with windows, overlooking smelting machinery where three Jackals, three Grunts, and an Ultra Elite are fighting troopers. The Jackals and Elites are fighting some cornered soldiers in the room below, and the Grunts are on a walkway on the right taking potshots at the troopers with you. Priority target is the Jackals, as the troopers they're fighting should be kept alive to keep the Elite distracted. Break the windows and shoot out the Jackals with your DMR (or needle rifle, but it will have to be needle combines instead of headshots.) When the Jackals are dead, head to the right and headshot the Grunts. Grab a plasma pistol from one of them and noob combo the Elite. Move quickly, because a Phantom will come soon carrying two more Elites, either Majors or Ultras. One has a concussion rifle and the other dual wields plasma rifles. If you retreat to the far right (the opposite side from where you entered), they might pass you by and focus on the troopers, letting you take them by surprise. When they're all dead, return for your DMR, needle rifle, and Spartan Laser and keep moving on.
Now comes what would be an extremely challenging battle: the Hunters. Two Hunters are in the next area protected by a team of Skirimisher Murmillos, and the only weapon you're provided to fight them with are assault rifles and shotguns. But fortunately, you've brought a trump card: the Spartan Laser. Hang back and headshot the Skirmishers while the enemies are distracted by Emile. Then when they're dead, snipe both Hunters with the laser. Aim carefully, because you've only got four shots and it takes two to kill each Hunter. Sometimes you might get lucky; the laser has small splash damage and might kill both Hunters at once if they bunch together. Then return for your needle rifle and move into the building ahead when they're all dead.
The Smelting Plant
The first half of the smelting room reverses your own strategy for the previous areas. Now you're on the bottom of the room while marksmen snipe at you from above. Three Jackal marksmen pick at you from the left balcony with needle rifles, and two groups of shield Jackals defend the right balcony and path to the stairs. But while they are annoyances who can be headshot easily, there's a more dangerous threat in the room: an Elite with an energy sword. On Heroic, he's an Ultra Elite; on Legendary he's a Spec Ops Elite cloaked with active camo. So you need to remain aware while counter-firing if he's coming or not. Don't stay scoped in for too long; check the area and even jump on top of one of the barriers with a crouch jump if you feel unsafe on the ground. There's a spare DMR to your left facing the balconies if you need it, and there's an ammo crate with more under the balconies.
When all the Jackals above are dead, move up carefully and grab a plasma pistol from one of the dead Jackals. Fall back, and the Elite should charge. If you're lucky, he'll focus on Emile and give you more time to repel him. Use the noob combo to kill him before he reaches you. Then grab your DMR and needle rifle and head to the top floor.
The upper balcony is shaped something like a rectangular donut. Walk along the side and scope in. You'll see a door on the other side open, letting in an Elite and three Grunts. The Grunts can easily be headshot as they're coming through the door. The Elite is more troublesome, as he's a dual-wielder and this balcony has long sight lines for him to spam you from. So after headshotting the Grunts, go to the left side to avoid his fire. There's slightly more cover on this side of the balcony, and you can collect a plasma pistol from the dead Jackals there to noob combo him. Stay in cover, wait for him to be distracted by Emile, then blast him.
Before you leave, refill any needle rifle ammo you might have used via the dead marksmen. There's roughly 35 to 44 rounds in the area, enough for two magazines. Refill DMR ammo too from below, then go through the door and up the stairs until you reach some Marines fighting a Jackal and two Grunts. Either headshot them or take them out with a plasma grenade (you may want to save your frags, as you won't get more in the next area). Even with a plasma rifle, the Jackal is no big threat.
Keyes (Rally Point Bravo)
Before covering the final battle, it's best to talk about the battlespace of this final area, the Pillar of Autumn's dock. The dock is comprised of five areas which are: a north landing pad, a west rock plain, an eastern rock plain, a center platform, and a two-story building stocked with weapons. The weapons base is likely where you'll usually be, but you'll have to move from there when enemies storm it. Since you can be attacked from any side, keep a close eye on your radar to be sure you don't get flanked. The many stairs can be used as cover and to throw off enemies' aim. There will also be some Marines joining you, but they'll all be killed in the final wave guaranteed.
As for weapons, inside the base you'll find assault rifles, grenade launchers, shotguns, and a few armor abilities. More importantly, there's a hidden crate with DMRs that will be absolutely vital. To get it, go to the back of the base and melee the wall or go inside and melee the small box inside. If the crate falls off the cliff or gets stuck inside, revert the checkpoint and try again. There's one more DMR lying around in the western plain, and a sniper rifle with twelve rounds on the roof of the base.
The last thing to know is that the waves come in based on enemy numbers. When there are two enemies left, the next Phantoms will come. If you need time to heal and grab ammo, leave three enemies alive at a distance. Emile will be in the mass driver above you, but he's just loud noise; none of his shots strike the Phantoms that actually land. The one way he's useful here is his voice cues. If he says any of the following lines quoted below, that means the next wave is coming.
Wave 1 lands as soon as you arrive. It consists of assorted Jackals and Heavies Grunts already on the ground, and two Phantoms carrying Brutes that fly in very soon after. When you enter the area, stay on your balcony and don't go down the stairs yet. Use your high ground to shoot down as many Jackals and Grunts as you can before the Brutes show up. When they do, stay back a little so they're distracted by the Marines. Use your DMR for this section; it isn't time to use your needle rifle yet. When you kill enough of the Brutes, they'll retreat from the center platform to the western plain. Use this opening to get the hidden DMRs and refill ammo.
Since there's only a few enemies left, your priority is to target the ones most likely to ambush you when Wave 2 comes. The most dangerous foe will be a Brute Captain with a Plasma Repeater, which is much faster and stronger than the Minors' Spikers. This Captain likes to stay far back in the western plain behind some boulders. Wait for him to come out of cover and then use the needle rifle; it'll be faster than five DMR headshots.
When there are only three enemies left, restock your ammo, look for plasma grenades, and head to the top floor of the weapons base where the Marines and sniper rifle are. Kill the last enemies and prepare for Wave 2.
Wave 2 is two Phantoms. One carries a pack of Brutes and lands at the central platform. The other carries Jackals and two Brute Chieftains, and it drops them at the eastern plain. Despite being further away, the eastern Phantom is the more dangerous. One of the Chieftains has a Fuel Rod Cannon, the other has a Gravity Hammer, and they'll charge straight for you after they land. But they're momentarily stunned when they land and you have a sniper rifle. That's your one chance. When the Phantoms fly in, pick up the sniper rifle, aim out to the eastern plain, and aim a little to the left of the boulder in its center. The Fuel Rod Chieftain will land, and it'll have two headshots to kill him. Then the Hammer Chieftain will land, and he'll take two headshots as well. Try not to use more than four or five shots (you'll need this sniper rifle again later), but make sure he's downed quickly.
If your shots miss or don't kill them, priority is the Hammer Chieftain as he'll reach you first. Don't panic, wait for him at the right stairs to your base, and stick with a plasma grenade. Once his shields break, shoot needles into him until he explodes. If you miss killing the Fuel Rod Chieftain, then don't use your sniper rifle, use your DMR to wear down his shields. Even though he's the highest ranking Brute in-game and has a ton of health, his shields are no stronger than a Minor Elite's. He'll either hang back by the plain or head to the balcony where you first entered the area. Break his shield then shoot three needles to detonate and kill him.
Once both Chieftains are dead, the only big danger is other Brutes possibly charging for your base. Take out Brutes with the needle rifle and keep an eye on your radar. Save the Jackals left in the eastern plain for last. You're going to have to abandon this base now for Wave 3, so head for that plain when it's down to three enemies left again. DMR or frag the Jackals, then turn in prep for the last Phantom wave.
Once again two Phantoms fly in, and the first one lands right above the base you were sniping from. The other lands at the western plain, so its troops will take longer to reach you. The first Phantom carries a Brute pack and the second drops in some Grunts and Brutes. Although the Brute pack has a Chieftain with a plasma launcher, his shots are very easily dodged. The greater threat is actually the Grunt team because one of them is a Heavy Grunt with a Fuel Rod Gun. Additionally both Phantoms blast down any remaining Marines, so you're on your own.
When Wave 3 arrives you should be at either the eastern plain or at the balcony where you first entered. Your loudout should be your needle rifle, DMR, and perhaps any plasma pistol from the Jackals you just killed. Hang back, maybe deploy your Drop Shield, and wait for the Phantoms to leave as they'll often shoot you with their chin gun and side turrets. Then start needling Brutes. The Brutes on top of the base will all be Minors, but keep an eye out for the Chieftain with them and any troops coming from the second Phantom, especially the Heavy Grunt. As soon as you see that Grunt, headshot or needle him him ASAP. The other Grunts will be Ultras and Majors, but they'll all have plasma pistols and so shouldn't be much threat. Feel free to use almost your needle rifle ammo in this wave and watch for Brutes that charge for you. When the Chieftain is in range, use a plasma pistol overcharge to drain his shields and then fire your needle shots.
When there's just two enemies left, Emile will radio Captain Keyes that the area is clear, unless the Chieftain is still alive. Kill anyone remaining and then gather weapons for the last fight of the level. Near Keyes' Pelican under the center platform is a good place to leave your weapons. Put the Grunt's Fuel Rod Gun, the Chieftain's plasma launcher, your needle rifle (what's left of it), and keep your DMR and sniper rifle with you as you go to the Pelican.
The final duel of the main campaign is now. Up ahead on the way to the mass driver is going to be three Sangheili Zealots, four or five Spec Ops Grunts, (on Legendary) an Engineer, and their leader a Sangheili Field Marshal. The Grunts will all have plasma pistols, the Zealots dual-wield plasma rifles, and the Field Marshal holds a Fuel Rod Gun. But as for you, you have all the weapons you just stockpiled before the cutscene plus more in the base. You're plenty armed.
After the cutscene ends, stand still but draw your sniper rifle, which should have at least one or two magazines left if you conserved its ammo. Look up at the door leading to the mass driver, where they'll be multiple Spec Ops Grunts and a Zealot waiting up there. Snipe the Zealot; it'll take three headshots on Heroic and four on Legendary. Wait longer, and another Zealot will step out and you can snipe him too. If you run out of sniper ammo, use your DMR to break his weakened shields. At this distance, he'll be too far away to shoot you or react to your shots. Then pick off the Grunts with your DMR before they flee inside; you'll need their plasma pistols.
Before going up the stairs and inside, it helps to drop carry your stockpiled weapons up there. If you want, you can also trade your Drop Shield for a Hologram from inside the base, and still top off DMR ammo should you need it. At the door you'll find the dropped plasma rifles and plasma pistols from the dead Elites and Grunts. These will also be useful.
Inside the base, there will be any remaining Grunts, at least one more Zealot, and the Field Marshal patrolling behind them. Headshot the Grunts, since at close-range they'll use their plasma overcharge and toss grenades. On Legendary, there will also be an Engineer floating above providing overshields to the enemies. If you still have needle rifle ammo, use that to shoot it. If not, use the plasma launcher with a locked-on shot or shoot with your DMR. As for the Zealot or Zealots, they're a bit trickier. Use the Hologram to lure them or use the Drop Shield if you head in then fall back. They tend to roam from the room on your left to the structures on the ground floor. If they go in the left room, use a plasma pistol-DMR combo to kill them. If they stay far back and try to shoot you while you're at the door, then use a plasma rifle to wear down their shields from afar.
That leaves the Field Marshal, the last and toughest of them all. Not only does he wield a Fuel Rod Cannon, but he draws an energy sword if you get too close, and his shields can resist one plasma overcharge. And he's got the high ground. The Noob Combo is still the best way to take him out, but you need to lure him close first. Use the Hologram to draw his fire so you can cross the room. When heading up to his balcony, send the hologram too first to detect where he is. It's also possible to ambush him, as the balcony has two stair entrances. He'll try to guard the one on the right, so consider sending a hologram there while you sneak past up the stairs to the left. When he's close, fire a plasma pistol overcharge and fire two DMR shots, one to break his shield and the other a headshot. If he lives and draws his sword, fall back immediately and try to combo him again.
The Mass Driver
With the Field Marshal dead, it's time to man the Mass Driver. In it you'll be engaged by multiple Phantoms and Banshees before aiming for the incoming CCS-class battlecruiser. While this section is easily done on Heroic and lower, it's much more luck-based on Legendary. In Legendary the Covenant's projectiles are so strong and travel so fast that often times it's impossible to complete this section in one go. So if you're worried things will go awry, enter and then exit the mass driver to trigger the Phantoms and hide by the stairs. Then when the cruiser arrives, run back up, deploy a hologram to distract all the dropships, jump in the mass driver, and fire a single shot at the cruiser to end the mission.
But if you're going to do this the hard way, then here's what to do. Two rules. First, prioritize Banshees. They may be smaller, but they're faster than Phantoms, have much longer range with their weapons, and one fuel rod from them will kill you. Second, check your blindspots every three shots. Phantoms that come from above or from the right tend to be harder to see and those are the ones that will cause you problems. And as an optional rule, don't be discouraged. If your shields recharge, that's a sign that you're doing good and can survive this bout.
As soon as you enter the mass driver, charge a shot and fire at the first Phantom you see. Fire at two more before looking up and shooting a Phantom coming from overheard. Then the Banshees will start to spawn from the left. Shoot at them then look up or to your right again for more approaching Phantoms. The general principle with Banshees is this: if three spawn at once, there's a good chance that you'll die or at least lose some health. If it's two, the odds are even, and below the odds are in your favor. Aim carefully to be sure you don't miss because the mass driver shots take a long time to recharge, about as long as the Spartan Laser.
After one minute and fifteen seconds of shooting dropships, the cruiser will lower its shield and charge its energy projector. At Keyes' urging, fire a mass driver shot into it to end the level and the Halo: Reach campaign.