343 Guilty Spark Walkthrough
From Halopedia, the Halo wiki
Part 01: Well Enough Alone
This is a lot vaguer place than any level in all the rest of the Halo series, keep your calm, nothing will attack you, just keep track on your motion tracker, use your flashlight sparingly.
Walk over to the downed Pelican. Fill up with the ammo, on Easy you will always acquire a Shotgun, but in Normal and higher difficulties, Bungie has removed it so just fill up the ammo and continue. In addition, if you are not on Easy the time when you will actually get the shotgun is much later in the level.
Move down the path through the big puddle. A little up ahead, you will find a couple of dead Covenant with two Plasma Pistols and one Needler. Ignore it; it's dead empty. On the other hand, those Plasma Pistols are fully charged. Swap your Assault Rifle for one of them.
There is a path leading up towards the ramp right up the Pelican Hill, there you would get an Active Camo, but it's practically useless unless you like to ambush some Grunts.
Move ahead and you should see another downed covenant dropship, the Brilliant Gift. There is a small group of Grunts and Jackals (about six in total). The Grunts are dumb enough to charge straight at you, so switch to your Human Pistol and kill them with a headshot or smack them in the face. The Jackals tend to stay back, so use your Plasma Pistol against them. Shoot each one with an overcharged shot, and melee them (to save Pistol ammo). Once they're gone, keep moving until you reach a sort of ramp made of a large tree root. There is a Jackal nestled in a crook on the other side, so feel free to use an overcharged shot and then melee it. Now go back for another Plasma Pistol.
Go across the tree bridge, and you should see a Shade on the other side. (When you are on the centre of the tree bridge, look to your right. You should see a large metal pipe. Jump toward it and hike up along its left side. Here, you will find one unit of Active Camo) Keep moving, and you should see an explosion, and another group of Grunts/Jackals being attacked by Marines. Feel free to start firing overcharged shots on anything that moves. Once the main group has been killed, go in and melee any remaining enemies. Now go back for your Assault Rifle.
By this point the Marines from earlier should have disappeared, leaving you on your own. Get on the lift and get down into this descend into the structure.
When you stop, switch to your Assault Rifle and get ready to fight. In the small antechamber, there is another squad of Grunts/Jackals. Less experienced players may prefer to toss a Frag Grenade at them, but you can also fire on the nearest Grunt to get their attention, then move through the other end of the antechamber and melee the first enemy in front of you, and repeat this method until they're all dead.
In the next room, grab a Plasma Pistol and send some overcharged shots over to the Covenant on the floor. Once most of them are killed, grab your Assault Rifle and get on the floor and beat the rest to death. Moving on to the next room, you'll see three Jackals; kill them. In the next hallway, you should see a dead Jackal, a lot of Covenant blood, and a small room full of mangled Covenant corpses.
Eventually, you'll come to a room with holes, plasma scoring, blood, mangled bodies, flaming wreckage, and a very frightened Marine. Now move to the other side of the room and you should probably find a fully charged Plasma Rifle. Swap your Plasma Pistol for it. Afterward, get onto the second level, into the next room, and activate the light bridge and move down the ramp.
An interesting thing to note is that when you return to the room the scared marine was in, in the next chapter, he will be oddly missing, with no blood and no signs of conflict with the Flood.
Part 02: The Flood
Load your game and take a good look around the room. There are six doors on the ground level: one behind you, one in front of you, and two on either side of you. To your left, there is a supply of Pistol and Assault Rifle ammo. Fill up on Assault Rifle ammo, and then go to the door in front of you.
Right about now, that door will bust open and a wave of Pod infectors will attack you. Note: if one catches you with your shields down, you're in trouble. But just slowly unload a few dozen Assault Rifle rounds into the main group and melee the survivors (no need to waste ammo). As you finish off the main portion, the door on your right is going to bust open too. Feel free to fire the rest of your Assault Rifle magazine into that swarm. The door on your left is going bust open now, and this wave is pretty big, so it may be advisable to toss a Frag Grenade to clear out the first couple dozen, and unload on the rest with your automatic weapon.
Now, the door you came through is going to bust open, revealing a bunch of Infection Forms and a couple of Elite Forms. Use the pistol on them. The Flood don't have shields, but they are very powerful, and you'll want to stay pretty far away from them. Use the pistol on the general area of their chest, as they don't really have a head to aim at. The tentacles also make a good target.
After a few seconds, that entire group of Flood should be dead. Head up the ramp you came in by, but watch out for more Flood combat forms just waiting to ambush you. If you see them, you could always neatly blast them in the chest with your M6D Pistol, but you may wish to fire the MA5B on full auto.
In the next room, a pack of Flood are taking on the Covenant. Stay on the upper level and exit through the door to the right. Head through the hallway to find yourself in another room full of Flood, and this time there is no Covenant to distract them from you. Stay on the upper level and back into a corner. Fire a few shots to get the attention of the Flood. They'll all gather into your corner, but not one of them will have the brains to try and jump up onto your upper level. Now, between the wall and the upper level, there is a tiny crack. Just big enough for a frag grenade! Throw your grenade through the crack. Drop down; clear out any survivors, and head through the door below the one you entered by. Follow the hall back to the previous room.
The Flood should be done with the Covenant here by now. Peek out of the hall, gun down anything close by with the M6D, and then retreat into the doorway. When the Flood come for you, use the Assault Rifle on them, and repeat as necessary. Head back through the blood-spattered hall to the door on the right. This next room has Covenant and Flood again. Wait a while for the entire Covenant to die, and then use the same strategy as before on the remaining Flood. Once everything is dead, jump up the stack of Covenant crates to get to the upper level. There might be a few Jackals or Grunts that hid from the Flood up here. Kill them with the MA5B.
There are two doors up here. One is near where the Covenant were. You will go through there eventually, but now you will want to power up the Energy bridge and head directly across to find the elevator you got down here on. They come at you in droves, but you can use the same strategy you've been using. Hold the doorway with the Assault Rifle and Grenades, and then kill the remaining enemies with a pistol. Quick! Activate The panel!whew...Elevator's outta the question.Time to find another way out.Preferably not broken.
Now, go back through the door the Covenant were at. Here there are no enemies, a load of ammo and health and the M90 Shotgun. The M90 is your prize; for the rest of the game, it'll be your go-to gun, as the pistol becomes gradually less effective and is a very effective weapon against the Flood.
After the next hall, you will come to another elevator room. This time, though, you don't need to camp in the doorway. You can use the Shotgun to kill the Flood here. Once you're done, hop on the elevator and descend downwards.
The elevator shaft's bottom can be a bit tricky. The Flood has got you surrounded here. Bunny hopping and using the Shotgun to kill the Flood here is arguably the best strategy. Head to the right side of the door climb up on the crates, and grab the Overshield as soon as the Flood are all dead. In the next room, there's a couple of Marines left. If you are able, you can save them, but mostly, you should just worry about yourself before anyone else. Grab one of the camouflages and start firing some shotgun rounds into the Flood down below, coupled with grenades whenever you feel one is needed. The Shotgun, despite its reputation as a close-range weapon, is actually pretty effective at long ranges too; you just need to aim carefully. After about a magazine from it, those Flood should be dead. Once they're all dead, grab the other Active Camo and head down onto the lower level. Exit through the blown-out door. The next split-path hallway has Flood hiding on either side, so be careful. If you get surrounded, you will be in considerable danger here.
The next room is pretty normal. Flood are on the lower and upper levels, but there aren't too many of them. Jump up on the flaming pile of rubble. Grab the ammo and health, and then jump up onto the upper floor. Leave through the only open door. Keep going straight across the next room. Enter the next room. You're on top with Flood below. Luckily, you can use the "grenade through the wall gap" trick again, killing most of the Flood here. Drop down and blow away the survivors, then leave through the broken door. The next room is more or less the same as the last one, only now you're on the bottom. A shotgun shell for each Flood form, and you're on your way again. Directly across the room from the door you came in by is an exit. You'll run into a load of Flood in this hall, so open up with the shotgun. You're about to get a chance to refill on ammo, so don't worry about conservation. In the next room is a fallen pillar with health and a lot of needles and shells on top. Stock up, then jump from there to the upper level. The next hall is clear of Flood.
There is a bridge switch in this next area, as well as a bunch of Flood on the ground floor. You could try and clean them out, but this is not advisable. Extend the energy bridge and go across to the door. A lot of Flood will come out, there are at least ten of them in the doorway, they're so bunched up that a couple of grenades can kill them all. Kill the remaining enemies with the Shotgun. Head on through once you're sure everything is dead. You will now find another elevator.
The elevator will move upwards through the level. There are a lot of Marines up here, roughly thirteen, and about half of them have Shotguns. The rest have Assault Rifles. One or two may have Plasma Rifles. You might as well kill them. They'll just die anyway once you exit the building, and it's good practice for multiplayer.
Stock up on ammo and health one more time and move out of the base. The Marines know where to go, but they won't last very long. A good rule of thumb here is to stick to the left. When you see a structure with big blinking lights, get close to it and stay close. The Marines, if they aren't already dead, will be soon. At this point 343 Guilty Spark will appear. He will then teleport you to the next level.
Interesting to note, by the way: It is possible for two 343 Guilty Sparks to appear in the cut scene— the one who's talking to the Chief and one floating aimlessly in the background. Although this is probably just a glitch.
Another "glitch" is the event is when one of the Marines aiding you is Sgt. Johnson, despite the fact that he is canonically believed dead for some time after. This has happened on a couple of occasions and is probably because his character model is counted as a normal Marine in Halo: CE. Privates Bisenti, Jenkins and Mendoza can also appear, despite having been taken over by the Flood.
If you stalls around extraction point more than 10 minutes where a structure with big blinking lights and holding position around small hill (Which can seen the hill where the Flood came from), you'll able to acquire Rocket Launcher after killing Combat Form. Usually the Rocket Launcher was wielded by Human Combat Form. Notice that Rocket Launcher has nowhere to be found on this level but if you keep stalling around structure with big blinking lights more than 10 minutes, you can acquire it although the chance was very difficult.