Cortana (level)

Looking for Cortana, the Human AI?

Cortana is the ninth campaign mission (eighth playable mission) of Halo 3.

It takes place in the Flood infested High Charity(a mobile planetoid station). Your mission is to find Cortana in order to activate the new Halo ring.

Upon completing it on the Normal, Heroic, or Legendary difficulties, the player will earn the "The Key" achievement and 40 Gamerpoints. Earning over 15,000 points in the campaign meta-game on this level will give the player the Orpheus achievement and 10 Gamerscore.

A curious note to add to this level is that if you listen carefully, Cortana will say some quotes by Dr. Halsey from Halo: The Fall of Reach. The Gravemind will also repeat his line "two corpses, in one grave" that he first said in the penultimate Halo 2 level - High Charity.

This level has been infamous among the community for being overly difficult, frustrating and generally not very fun, along with Combat Evolved's The Library. The entire level is covered with Flood 'sludge', which is thought to be flesh of dead bodies. This means that enemies easily blend into the scenery, thus making the level very difficult. Some fans have even claimed it is one of the worst Halo single player missions ever made and a few have even labeled it as the 'worst video game level ever designed'. In contrast, other players enjoy the level for its challenge. A few players have commented that the levels layout is simply too confusing for those playing it the first time. This is because the enormous amount of enemies and maze like pathways. Despite all this, many praise Bungie for making this as realistic as possible.

Transcript
{Cutscene}

''The Master Chief flies a Banshee to High Charity. He finds an opening into the hive. (In co-op, Thel 'Vadam will follow the Chief and land his Banshee next to the Spartan's Banshee)''


 * Sergeant Major Johnson (COM): "Chief, I'll round up our survivors, fall back to the Dawn."

Master Chief drops down onto a wide platform from a hole above ('Vadam follows him in co-op)


 * Johnson (COM): "Arbiter will do the same with the Elites."

-(Co-op Change) Johnson (COM): "Shipmaster will do the same with the Elites." (Note there are no subtitles for this line, since the text varies)

The Chief shakes off the organic material that is stuck to his boot.


 * Johnson (COM): "Cortana's in there somewhere..."

Rampant
Graverobber.

{Gameplay}

Chief begins searching, further in the hive.


 * Gravemind (Gravemind Moment): "Child of my enemy, why have you come? I offer no forgiveness; a father's sins passed to his son."

A little later.


 * Cortana (Cortana Moment): (A strange mix of cries of agony and maniacal laughter)


 * Cortana (coming out of a speaker within a crashed Pelican): "I tried to stay hidden, but there was no escape! He cornered me, wrapped me tight and brought me close."

As the Chief goes deeper into the hive.


 * Gravemind (Gravemind Moment): "Of course, you came for her.... We exist together now. Two corpses, in one grave."


 * Cortana: (sounds distant, then when "stolen" is said, sounds suddenly close) "A collection of lies; that's all I am! Stolen thoughts and memories!"


 * Gravemind (Gravemind Moment): "And yet, perhaps a part of her... remains?"


 * Cortana: (deranged laughter)

''In the large room where the Tilt skull is located, a Terminal can be activated, but does not count towards the Marathon Man achievement. If activated, it displays another Cortana Moment)''


 * Cortana (Terminal): It was the coin's fault! I wanted to make you strong, keep you safe (drop in tone). I'm sorry, I can't...

(Reference to earlier sections of Halo: Fall of Reach in which Doctor Catherine Elizabeth Halsey examines John-117 as a potential Spartan II candidate)

Cortana begins to show clear signs of malfunctioning.


 * Cortana: (casually and kindly, as though nothing is wrong) "May I speak with you, please? ... What's your name? It's very nice to meet you! ... You like games? So do I."

(Also reference to earlier sections of Halo: Fall of Reach in which Doctor Catherine Elizabeth Halsey examines John-117 as a potential Spartan II candidate) The Chief struggles through into more narrow, Flood contaminated tunnels.


 * Cortana: (upset) "I'm just my Mother's shadow... don't look at me, don't listen! I'm not who I used to be..."

As the Chief nears a large room {with the route to the reactor room at the top}.


 * Gravemind (Gravemind Moment): (angry) "Time has taught me PATIENCE! But basking in new freedom, I will know ALL THAT I POSSESS!"

En route to the reactor room.


 * Cortana (Cortana Moment): (Panicking, her voice slightly distorted) "I have walked the edge of the abyss. I have seen your future, and I have learned!"

The image of Cortana suddenly turns a tinge of green, and clutches its head and writhes in pain.


 * Gravemind (Gravemind Moment): (Shouting angrily.) "SUBMIT! END HER TORMENT AND MY OWN!!"

The Chief enters the reactor room, passing by bones and skulls back at the entrance.

The Chief finds a door out of the reactor room, and follows it.


 * Cortana (Cortana Moment): (Panicking, voice slightly distorted) "There will be no more sadness, no more anger, no more envy!" (a possible reference to the three main stages of rampancy.)


 * Gravemind (Gravemind Moment): "You WILL show me what she hides, or I shall feast upon your BONES!"

The Chief begins to reach the end of the hallway.


 * Cortana (Cortana Moment): ''(Speaking in a distorted monotone voice as though brainwashed. Her image is green.) "This is UNSC AI Serial Number CTN 0452-9. I am a monument to all your sins."

''The Chief rushes to the end of the hallway, to find Cortana lying prone in a Stasis Shield in a center podium. The room resembles the Sanctum of the Hierarchs. He beats and bashes the shield until it finally fails.''

{Cutscene}


 * Cortana: (weakly) "...you found me..."

''Master Chief leans closer towards the panel Cortana's on. The AI lies pitifully on the podium, with an expression of pain, suffering and shame on her face.''


 * Cortana: (weakly) "But so much of me is wrong... out of place. You might be too late..."


 * Master Chief: "You know me. When I make a promise..."

She looks up at the Chief.


 * Cortana: "...you... keep it. (she raises her head, and sounds amused) I do know how to pick 'em."


 * Master Chief: "Lucky me. Do you still have it?"

''Cortana slowly gets up, recovering her strength. She opens her palm and a hologram of the Index floats above her hand.''


 * Cortana: "The Activation Index from the first Halo ring. A little souvenir I held onto... just in case. (she looks around) Got an escape plan?"


 * Master Chief: "Thought I'd try shooting my way out - mix things up a little."

''The Chief takes Cortana's old data chip out of his helmet and holds it in front of her. Cortana touches its core and uploads herself into the chip, and the Chief inserts Cortana back, at long last, into his armor.''


 * Cortana: (jokingly exasperated) "Just keep your head down... There's two of us in here now, remember." (This is a reference to Halo: Combat Evolved, where Cortana would say "Keep your head down, there's two of us here now, remember?!" When the Master Chief first loses a health bar on the first level, Pillar of Autumn.)

Nor Hell A Fury...
Shoot your way out.

{Gameplay}

If the Chief continues to stay in the room Cortana was in.
 * Cortana:(weakly) "Chief, get me out of this place. I... I don't want to stay."

The Chief heads back up the hallway.


 * Gravemind (Gravemind Moment): (roars) "Now, at last, I see! Her secret is revealed!"

The Master Chief makes it back into the reactor room.


 * Cortana:(weakly) "Wait, we need to buy some time. This reactor... start a chain reaction. Destroy High Charity."

''The Flood begins to swarm the reactor room, realizing the Chief's plan. However he successfully destroys all three reactor pylons.''


 * Gravemind: (Roars in pain)


 * Cortana: "You hurt it, Chief. But not for long. We need to get to Halo - destroy the Flood once and for all."

If the Chief takes too long
 * Cortana: "An explosion just made us an exit! I'll mark it on your HUD, Chief, go!"

When the Chief reaches the halfway point escaping.


 * Cortana: "Analyzing the route ahead... I have it mostly figured out. Just keep moving, I'll update your HUD as you go."

Cortana: "Corridors ahead have all collapsed. I'll find another way, Chief; be careful."


 * Cortana: "There, Chief, into the maintenance tunnel."

The Chief finds his way back when...

(Single-Player Only'')
 * Cortana: "I've got a friendly contact! But who would be crazy enough to come in here?"

''Chief and Cortana find The Arbiter battling Flood with a Flamethrower. The Chief assists.''


 * Cortana: (Amused) "Wait, you two made nice?! What else have you been up to while I was gone...?"

{Cutscene}

The Master Chief and The Arbiter find a Pelican, possibly from the In Amber Clad'' nearby and board it. The Chief uploads Cortana into the Pelican's holotank and starts up the engines. One of the Gravemind's tentacles advances to the Dropship, but the heat from the thrust forces it to retreat. The Pelican takes off, smoke pouring lightly from the left engine. The tentacle comes back and tries to wrap around the Dropship, but the Chief escapes its grip. The Pelican barely escapes from a massive explosion caused by the reactor going critical as High Charity is finally destroyed, and the Pelican makes its way to the new Halo ring.''

Walkthrough
The recommended active skulls on this mission are Tough Luck and Catch. Tough Luck doesn't have much of an effect since the room for the Flood to evade your grenades is limited. As for Catch, the Flood doesn't use grenades, so it's a consequence-free multiplier.

Please also note that the Flood-infested High Charity is a completely different environment to the one visited in after being teleported by Gravemind in Halo 2. It is disturbingly easy to lose your way, so always keep attention. Beating this mission is a matter of measured progression and the right weaponry is essential. The Brute Shot, Energy Sword, Shotgun, Plasma rifle and Gravity Hammer are highly recommended weapons for use against the Flood in this mission. The confined spaces make for several close-quarters battles, so a good Melee weapons can always be useful. A key irritation in this level is the amount of Ranged forms that hang from the ceilings, so carrying a medium-to-long ranged firearm is also essential.

SEARCH FOR CORTANA Drop down and fire upon the Infection Forms. Unless you're actively seeking a higher score, make sure they do not animate any of the corpses nearby. Replace your Assault Rifle with a Plasma Rifle and collect some grenades prior to moving on. Plasma-based weaponry is more effective against shielded Combat Forms, should you encounter any. Throughout this mission, take care not to shoot the fleshy sacs on the walls. They will release Infection Forms if hit with anything other than a direct Flamethrower burst.

As you round the corner, a few sacs filled with Infection Forms will automatically explode. Eliminate them quickly so that they don't re-animate any bodies. Head up the sloped path to reach the chamber's upper level. Find some grenades and grab a second Plasma Rifle to dual-wield with the first. Also replace your Shotgun with an Energy Sword.

When you reach the portal in the floor (these round sphincter-like orifices that act as doors), drop through it and immediately take cover in the corner behind you. After a moment or two, Combat Forms will move into the open. Blast them one-by-one with your Plasma Rifle, ducking back into cover if your shields are down or if your weapons have overheated. After the Combat Forms withdraw, Carrier Forms will begin waddling towards you. Destroy them with grenades - the Plasma and Incendiary varieties work best. If you can find a Brute Shot around here, take it in place of the Plasma Rifles.

Expect to find many Pure Forms and Combat Forms on top of the fleshy hill. The best tactic here is to dash over to the crashed Pelican straight away. The journey there could be a bit fraught, but you can find useful equipment there, the Flamethrower in particular. It'll make the battle much less difficult, especially on higher difficulties, so a good idea would be to grab it. if you're lucky, the Flood won't follow. Take camp there, luring Combat Forms and Pure Forms towards you. The latter are easy prey for the Flamethrower.

Be cautious as you leave the Pelican, Pure Forms and Combat Forms might be still lurking around. Run to the other side of the hill, and make your way to the chamber exit. Note that a slope to the left of the portal leads to an upper level where you can acquire two Plasma Grenades and an Incendiary Grenade. The next corridor is empty, and easy to find your way through.

The room after that contains a small slope and several Infection Forms. The chamber is filled with dead Elites and Brutes, as well as some grenades. Pick these up to replenish your supply. Use short bursts of flame to avoid the re-animation of Combat Forms. You can throw a grenade to set off a chain reaction and weaken or kill those which do rise. In the next tunnel, either grab a Gravity Hammer or Energy Sword (your choice), then drop through the hole to continue.

After you pass through the entrance, head straight to the left. This area provides cover from a group of Ranged Forms as you dismember the first wave of Combat Forms. Operate from here, drawing the Flood to your position.

Another way to beat this mission would be to use a better player to escort you in Co-op. You follow them and do not stop to take out anything just run to each point. Keep the Energy Sword handy if you run into some trouble but you can take whatever weapons you feel like. This only works on lower difficulty and you will still die a lot.

Shotguns are also very useful, but ammo is very limited. Use it until you make it to the crashed pelican, get the ammo, and make sure you have an Assault Rifle/SMG or Plasma Rifle to take care of swarming infection forms. Also pick up the Flamethrower to incinerate anything in your way!

Speed Run Walkthrough
Out of every campaign level in Halo 3, Cortana is normally judged as the most difficult. The endless amounts of flood that attack you and the limited amount of ammo you have determine the difficulty of this level, and on Legendary it will be nearly impossible to tackle this task.

Many people have attempted to beat this level by actually fighting their way through the level-and as some may have completed it this way-it will be a challenge that only the best of the best can complete. Many people take a strategy that some call cheating, being lazy, etc. but it is by far the strategy that will provide the best results in the end.

This is called the "Running Man" strategy, where instead of fighting the flood, you simply run as fast as you can through the whole level, and with a little luck your life will be a lot easier.

When the level starts, you will spawn with a shotgun. This will be useful for a short while, but we will swap it out later. Progress through the infection forms running, don't waste your ammo on them. Once you get to the point were the combat forms spawn, throw a frag grenade at them and they should all be dead. Continue running, and then you should get to the point were you drop through the hole in the floor.

Once you enter here, you will be bombarded by flood. I would actually fight these, because normally there is one with an energy sword, which will definitely come into use later on in the level. When the carrier forms attack you, throw a firebomb grenade and you will be able to skip the infection forms.

The next room is one of the most difficult places in the level, so be prepared to keep at it for awhile. First of all, when you get to the nav point a convoy of flood will attempt to kill you. This is were the running man strategy comes into play. On the left wall, there is a pelican on the ledge, and in this pelican is both a flamethrower and a rocket launcher. I strongly recommend swapping out your shotgun for your rocket launcher, because it will be vital for completing this level.

Once you get your weapons, run as fast as you can through this room, jumping at every second and avoiding the flood at all costs. It may take awhile, but eventually you should reach the end. Near the end door, there are a few carrier forms, so be aware of the fact that if your shields are down they will kill you fast.

Once you get to the end, you get to a room with a few regenerating flood. In the room somewhere there is a Brute Shot, so swap out your energy sword for the Brute Shot.

Once you drop through the hole in the floor, you will enter another difficult point of the level. There are loads of flood, mostly pure forms that change into ranged and tank forms, that will all be trying to take you down. For the ranged forms that stick to the walls, I recommend taking them out with a shot of your rocket launcher, and try to kill the tank forms with your Brute Shot.

Once you are able to hopefully get to the center of the room where the Tank Form is, there is what makes the level a vacation for you. Near the center of the room, there is a cloaking device, that allows you to skip through a part of the level undetected. Get this now, because the next part is going to be determined by how you use you rocket launcher and your cloaking.

Once you reach the thin hallway that leads to the room with the 2 carrier forms, be sure to take them out with your Brute Shot and destroy whatever else enters the room. Then, instead of running through the bottom where the flood have an advantage on you, there is a small ledge before you enter the room where you can actually got through the room on the roof, which give you an advantage.

First off, I hope you still have the cloaking, because you definitely need to switch it on here. There are endless amounts of combat forms that come out of the exit, and unless you attempt to take them all out with your rocket launcher, which is very possible, you will need your cloaking to survive, because there about 8 other pure forms in the room, and are normally transformed into ranged forms.

Once you exit this room, check your ammo to make sure you aren't out. By now, you are nearly done with your rocket launcher, so if needed you could swap it out if on low or no ammo. As far as your Brute Shot, keep it for sure.

The next room is another annoying part, so be patient and prepared to be at it for awhile. First off, it is the same story as the last room, cloaking is necessary. In one of the narrow hallways there are 2 cloaking devices. First off, get one and use it to progress to the end of the room. For the second one, keep it for later.

Once you get near the door, your cloaking will wear out, so if your shields get down, definitely use the second cloaking. Run to the next door, and pick up the Brute Shot ammo next to the door.

After the long path to the area were you get to save Cortana, there are plenty of flood there, but it is not nearly as difficult as the first challenging room.

When you get there you should be on a ledge with a few pure and combat forms, so try to take them down with your brute shot. When you get to the middle of the room, try to take some of the flood down from range. There are lots of places for cover here, so use them when you are close to death. Then on the opposite end of the center tile, there is another cloaking on the right end. There is also a ranged form here, so strafe and jump to avoid being killed. When you get the cloaking, hurry to the door were you save Cortana.

When you reach Cortana, simply melee the glass globe that she is in and watch the cutscene.

After the cutscene, you will find yourself back in the same area you where in before. Now you have to work your way to the center tile and press the button that will open a few things that you have to blow up. While fighting off the flood, get out your Brute Shot and shoot at the nav points on your screen. One shot should do just fine. If you get down on health, activate your cloaking.

After this, you have to run out of the room and in to the same room you where in before. If you notice, you are going in the same path you were to get to this area, but backwards instead of forward.

Once you get to the hole in the floor, take out the combat forms with your brute shot and stay on the top always. Just keep running and running, and try to kill all of the flood in your way.

Once you finally get to the room were you got your first cloaking, try to take it slow and kill the flood one at a time, because a lot of them have brute shots and shotguns, and they could kill you quickly.

Once you break through the wall of flood, keep running and running, and eventually you will reach the first room that all of the flood have attacked you in. If you listen, Cortana will mention something about a "friendly contact" and you will notice that the Arbiter has joined you, with a flamethrower. Just simply let him do the killing, and run past all of the flood to the Pelican where you got your rocket launcher at. Go in the Pelicans troop bay and the mission will end.

Legendary Walkthrough
Cortana is probably the hardest level in any Halo campaign game. But it can be beaten by a good player. The secret is to make the most of what you have.


 * Know how to use every weapon to its greatest effect.
 * Unless you have beaten the level on lower difficulties, keep your MA5C, no matter what. You'll need its compass.  There really isn't any weapon that is weak in all situations.  The only exception is a Plasma Pistol overcharge—while it takes out Brute armor very effectively, it does little to the Flood.  If you get a Plasma Pistol, use normal shots.  The Flamethrower uses approximately the same amount of fuel for killing a Combat Form as for killing a Pure Form; therefore, save it to kill Pure Forms.  Human weapons provide an advantage if you are using a Deployable Cover in that you can remain where you are--safe--and fire on the enemy.  Spikers are particularly effective against Ranged Forms.  Don't hoard weapons continuously, despite how much you may think you need them--if you hoard too many, you will overload the map.  The most common result is that some weapons disappear or fall through the floor.  But if you are trying to beat the level with Iron or else with minimal death, hoarding weapons is your best bet, although it is time-consuming.


 * Know how to use grenades.
 * Try to use most of your grenades, but keep at least 2 stickies (anything that is not a Frag). These are particularly effective against Carrier Forms because they kill not only the Carrier Forms themselves, but also the Infection Forms inside them.  If you are having trouble killing something, say, a Pure Form in the large room near the halfway point, go ahead and throw a grenade.


 * Know how to use equipment.
 * If you are a Halo 1/2 veteran, you probably made it this far, with difficulty, without using equipment. But on Cortana, equipment becomes a necessity.  Deployable Covers are probably the best equipment; they do not self-destruct after a while, unlike any other equipment, and you can fire while protected if you are carrying a human weapon.  Note:  The Carbine cannot fire through Deployable Cover.  If you cannot find Deployable Cover, use a Bubble Shield, as lesser forms enter your shield, you can kill them without worrying about exposing yourself to Ranged Forms.  But when the timer goes out, you will be exposed.  The Cloaking is only good for speedruns.


 * Have good aim.
 * Conserving ammo is of course an issue, and killing enemies quickly has always been an issue. But there is now another penalty for missing:  you may hit a Flood Growth Pod and release Infection Forms as a result.  These can reanimate corpses that you have not yet destroyed, or they can finish you off after you take cover from several Ranged Forms.  Be sure all of your shots hit the enemies.

Skulls:


 * Iron
 * Not recommended due to the length and difficulty of this level. If you do use it, hoarding weapons will work well, although it will extend the time required to complete the level to several hours.


 * Black Eye
 * There are no Regenerators and many Ranged Forms. Not recommended.


 * Tough Luck
 * A consequence-free multiplier; the Flood don't dodge.


 * Catch
 * Activate this skull if you have it; the Flood don't use grenades, but they will drop more when they die.


 * Fog
 * You will be surrounded very easily. The least recommended skull.


 * Famine
 * Low enough ammo as it is. Not recommended.


 * Thunderstorm
 * Nearly consequence-free; a few more shielded Combat Forms are all that will result.


 * Tilt
 * Will nerf Plasma Rifles, which are otherwise very useful. Not recommended.


 * Mythic
 * Will result in consumption of more ammo. Not recommended.

Anyway, now on to the walkthrough:

Part 1: Rampant
You start out with an Assault Rifle and a Shotgun. Advance through the first room; you will encounter weak resistance. Be sure to melee corpses when you have killed them, just in case you accidentally burst some Growth Pods.

The second room contains the first Pure Forms of the level, but not yet. Kill the Combat Forms, then walk up the ramp. At the top, you will aggro a CQB weapon Elite form and several Stalker Forms. Quickly kill the CQB-weapon wielding form and take its ammo if it does not involve taking chances. The stalkers will transform into Tank Forms in most cases; retreat to the ramp and pump rounds into them until they die. Sometimes they will convert into Ranged Forms--a few melees often will kill them. If it is unsafe to melee, a Plasma Rifle works well because it will kill a Ranged Form before it overheats as long as every shot fired hits and the rifle was not recently used. Stick the Carrier Forms (it is best if you use a different grenade type for each). Then deal with the rest of the Flood in this area. You will need most of the weapons you obtained and several grenades. Pick up the Deployable Cover, but keep it. The rest of this section is easy until the one-way drop. “Walk” all of the weapons in the area into the drop, then drop down. To walk weapons, continuously run and hold RB, momentarily releasing the button whenever you pick up one of your weapons. This takes some finesse, but you will quickly get used to it. But before you do this throughout the level, please read what I said about hoarding weapons.

Deal with the immediate Flood threat, then rush forward and set up your Deployable Cover. The best place for it is to the left of the weapon drop pod, angled 45 degrees to the left. Alternatively, fire from the intersection-room if you have gathered weapons from the previous section. Use your MA5C or another human weapon to take out the Pure Forms (you can shoot through the cover itself from your side). If the Flood gather into a tight group, save some ammo and throw a grenade. Run past the cover to the back; it is safe and has a few Plasma Rifles as well as another Deployable Cover. Pick off the Ranged Forms (use your binoculars to track them down). When they are all wasted, take note of the weapon cache below you because you will return to it several times. Run off the center of the cache; the path ahead leads off of this room slightly to the right of the wall you face. But before you do so, get the Tilt Skull if you would like.

Stick the Carrier Forms and the Ranged Form. Be careful with the Growth Pods. The next room is quite elongated and contains several Ranged Forms as well as Combat Forms. Look up and to the left—the arch is a good place to deploy your Cover. Pick off the Ranged Forms. When the Combat Forms show up, retreat while pumping rounds into them. Throughout your progress through this room, you will probably make several trips back to the cache in the last large room. You will also find two Deployable Covers there. Use grenades as necessary. After the room is clear, look to the right of the entrance; you will see a destroyed hallway with a panel blown off. Enter the service corridor and you will find an M7057 Flamethrower. For as long as you have it, save it for Pure Forms.

After this, go through the Porta into the next room. Burn any Stalker Forms you find, but when the Combat Forms show up, switch to your small arms. There is a tunnel structure to the right where you can take cover. Using a Carbine and a Spiker, kill all Flood in the room. First worry about immediate threats, then Stalker Forms, then Ranged Forms, and finally Combat Forms. There are three levels to this room, and you will have to make two jumps. Fortunately, you can make both with your Flamethrower. Continue through the next room with the bones (surprising, considering the fact that the Flood need calcium); there will be no resistance.

Enter the reactor room. Turn right and advance, burning any Pure Forms in your way. Kill all of them. If you were frugal with your Flamethrower, it should burn out sometime around now. Cross the reactor core, then go through the doors. You should see that the Flood infestation is quite limited in this area. Cortana will turn green and say, “This is UNSC AI Serial Number CTN 0452-9. I am a monument to all your sins.” Enter the Sanctum. Cortana is in the center—beat the barrier surrounding her until it fails (2 swings of an Energy Sword or 1 hit of a Grav Hammer).

Part 2: Nor Hell A Fury
Watch the cutscene, then return to the reactor room. A Bubble Shield will be useful here; kill the Tank Form to the left and the Ranged Forms to the right. If, instead, you have a Deployable Cover, place it so that it shields you against the Ranged Forms. A Tank Form's hit can quickly destroy Cover, but the Cover is immune to the Ranged Forms' projectiles. Similarly kill all of the other Flood in the area. Prioritize: first anything nearby using an Energy Sword, then any Pure Forms, and finally Combat Forms. Destroy the pylons (the nav points will help you).

Drop down into the earlier part of the level and kill any Flood you see while retreating. Continue through the level, generally the reverse of how you entered. You will encounter minor Flood resistance. When you get to the room where you first fought Pure Forms, look out and you will see a damaged Pelican. Run to the cockpit of the Pelican to complete the mission.

Trivia

 * The Mausoleum of the Arbiter can be seen in the distance when standing near the crashed Pelican. This and the Prophets' Inner Sanctum are essentially the only recognizable features of High Charity in Halo 2 that can be seen in Halo 3. One can see in the Bungie feature "Flood Autopsy", that they had originally planned to have the Flood re-animate all Arbiter corpses in the room, creating an Arbiter army for the player to fight.
 * Nearly all of the Cortana Moments are quotes from The Fall of Reach, such as at Crow's Nest it is a direct quote from the speech Dr. Halsey, and many in Cortana (level) involve or are quotes from the genius, Dr. Halsey.
 * If you enter the crashed Pelican when first making your way through, you can hear Cortana's voice.
 * The section of the level after saving Cortana is called 'Nor Hell A Fury...', referencing the poem by William Congreve 'The Mourning Bride'. The entire line is 'Heaven has no rage like love to hatred turned, Nor hell a fury like a woman scorned', possibly referencing Cortana, who, after months of torment, now has the ability to light the newly constructed Halo ring and destroy the Ark, as well as the Flood.
 * Thematically, this level also has much in common with the levels Keyes and The Maw. It depicts the Chief venturing alone into a vessel to rescue a comrade or friend, from the Flood, most specifically for a data construct in their possession; and detonate the fusion reactor core. In this case the objective is the Index to fire Halo; in Keyes it was the Captain's neural implants to destroy The Pillar of Autumn.
 * The room where Cortana is located, is a remake of the room from the level High Charity from Halo 2. This room is located before the final gravity lift, where Cortana says, "Apparently these are the Prophet Hierarch's private quarters, their inner sanctum". In the "inner sanctum" there are three doors, two located opposite one another, with a third, opposite a large view screen. In the level High Charity, the Chief enters through the third door, and exits through the door on his right; in the level Cortana from Halo 3, he enters through the door that was locked in Halo 2 (opposite the door that leads to the final gravity lift). The graphic design of the room and the rest of High Charity's interior has been remodeled in Halo 3. It resembles the corridors of the CCS-Truth and Reconciliation from Halo: Combat Evolved.
 * The Tilt skull can be found on this level.
 * There is a area with a dead ODST (not the crashed Pelican). It is unknown how he made it so far from the Pelican or if he was from the Frigate In Amber Clad before the Flood attacked High Charity. There is also a Flamethrower in this area which hints to a final stand since he's in a pipe area with one opening.
 * After obtaining Cortana, there is a skull on a ledge-like structure (It's purple and is kind of bulbous at the end) overhead after you exit the hallway that lead to Cortana. To get it, you need to get the Deployable Cover, deploy it on the floor directly in front of the edge of the roof, jump on the deployed cover and crouch jump onto the roof. Once on top of the roof, locate the skull towards the apex of the angled roof and get the skull. Please note that this skull has no affiliation with the "13 required skulls" list and, if carried for the rest of the level, will start Master Chief with a Spartan laser on the next level. This may only work with certain skull combination's and/or other factors in game play.
 * One of Cortana's lines, "There will be no more sadness. No more anger. No more envy," appears to reference Marathon's stages of Rampancy; Melancholia, Anger and Jealousy respectively.
 * The line "It's the coin's fault," is a reference to where John was brought into the Spartan program. He identified the side of a 20th century quarter that was about to the hit the ground before it did in Halo: The Fall of Reach.
 * On single-player campaign at the end of the level, go out to where the Pelican is, and look to your right. You will see the Banshee the Arbiter rode in on. While you can get to it and destroy it, you cannot enter it, and oddly, grenades will not stick to it.
 * Much of High Charity is flooded with water; the reason for this is that it crash-landed in a large body of water near the Ark's Control Citadel. This can be seen by going out to the crashed Pelican and looking towards the Mausoleum and looking downwards.
 * Sometimes in the level, you will walk above a room where Infection Forms are running on top of each other.
 * In co-op, after saving Cortana and destabilizing the generators, if one player stays behind in the hallway with the hole, the generator room will disappear and the room will be replaced by the other player's point of view.
 * The Flood Portas have 7 parts, a direct reference to the number seven. There are also 7 Portals in the level.
 * During the level, you will find dead Elites wearing Assault Armour. One of them should be glitching by doing his death position in mid-air although; it looks like his foot seems to be stuck on one of the corrupted Flood rock-like. If you stick his body or deck it, the corpse will fall. That is the only way except for a Brute Shot grenade or other explosive.
 * This is the last level to not have any usable vehicles at all.
 * Many Elite bodies in this level wear Assault Armor, which is strange because Elites never wore Assault Armor while in the Covenant.
 * This is one of the most unpopular levels.
 * If you finish the previous level with an energy sword and rocket launcher, both with ammo remaining, you will start this level with no weapons at all.
 * This level and Keyes are named for the character you need to achieve to help you destroy Halo.  Also, the primary enemy in both levels is the Flood.
 * This level was originally split into two separate Campaign missions, both considerably shorter than the current level.
 * It is near the lines of being impossible to do this level on Mythic.
 * The acheivement Orpheus is a refrence to mythology, a person named Orpheus went to the underworld looking for his wife, similar to cheif looking in Gravemind for Cortana.
 * According to a quote made by Bungie developer Jason Keith, found in and, it is implied that the Flood Hive of High Charity and the Gravemind were one and the same during Halo 3, thus making this level seem like a boss fight, in a sense.
 * It is odd that the weapons next to bodies in this level are usually found with a full magazine or charge, as their owners were probably fighting when they died.