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Look up, immediately. A Drone swarm will descend upon you from holes in the roof, followed by a pair of Elites from the right. Try and get into the top right door and use your sword to cut the Elites down as they spawn. Note that one of the Elites is a Major, who you will have to lunge and finish with a headshot.
Once they're dead, another pair of Elites will spawn in the hall; give them the same sword-and-headshot technique. Often, a Major Elite will run into the hall from the outside, but he should fall just as easily.
This next area, though, can be pretty tricky. There are five or so sniper Jackals inhabiting the area, not to mention another group which will show up a bit further on. The safest idea is that when you exit the door, stop and look around for a Type-50 particle beam rifle, outside the exit to the right. Take out the snipers and then start working on any Elites you happen to see.
Keep going and you'll run into a number of Grunts and Elites guarding a bridge. If you've taken out all the snipers it shouldn't be TOO difficult. If you haven't taken them all out, however, expect to have a Type-50 particle beam rifle shot at you, so be sure to double-check the area before engaging. When you get to the far side, there will be one Elite Minor in the outer wrap-around hallway, then a room full of Grunts and Jackals all armed with Plasma Pistols; it's not hard to kill them all if you stun them with one shot and melee them to death (to save precious ammo). If you are using a Carbine or want a Carbine at this point, there's a pile of blocks semi-blocking a walkway outside. You can jump on and crouch-walk-through, and there are two Carbines (pick up one and snag the ammo of the other) and two Plasma Grenades if you're running low.
Hold on to your Type-50 particle beam rifle; there are many sniper Jackals and some Elites in the next area, but they are next to an opening, so they don't have a lot of cover. Take out some of the snipers and one of the Elites (likely a Major) from the cover of the pillars just outside the Jackal-Grunt room, then close in and just melee the rest of the sniper Jackals and kill the Elite Minor (sticking is recommended, it's really easy to). Switch your Type-50 particle beam rifle for one with more charge and head back through the doorway where you entered the open area. In a second, a Phantom will pull up and drop off two Hunters. However, with your new Type-50 particle beam rifle, you should be able to put out two shots before they react. You can either choose to kill one of them or wound both.
Alternatively, in the very first room of the level, you could kill all the enemies, circle around to the left upper level, jump on top of the pillar that should be holding up the roof, jump over to the ledge above the door you came in by last level; from there, grenade jump up onto the ramp; from the top of the ramp, grenade jump onto the roof; from there, grenade jump to the far area with the five snipers. The bad thing about this is that it cuts you three grenades and puts you in a pretty bad position to deal with the snipers and Hunters. Oh well.
Once you have taken out the Hunters (for which is recommended to take the shotgun from one of your marines if you haven't already) a Pelican will show up, dropping reinforcements as needed, as well as a few weapon pods. At this point, give your Marines sniper weapons, and prepare to face the motley crew of the gondola, which consists of a Lance and an Elite and maybe more than two Jackals. At the range you have, they shouldn't pose much of a threat.
Once the gondola is secure start transferring weapons out of the drop pods and into the gondola. You are going to be wanting as much firepower as you can get pretty soon.
02: One Way Ticket
Soon, a Drone swarm will buzz in to attack you from behind, but the sniper Marines will make short work of them. The gondola that passes you, however, also has a Drone swarm to complement the two Elites on board, so you may want to chip in there.
As you approach the far side, you could elect to sword-fly up to above the entrance, using the turrets, but I wouldn't advise it; the gondola will not dock if you do so, and that means losing your Marines. Therefore, I find it works better to just exchange your beam rifle for a shotgun and use it to blast your way through the next area. There are two sniper Jackals and seven regular Jackals, not to mention a Drone swarm which will spawn further up in the room once you've killed the Jackals, but they shouldn't prove too difficult for a grizzled veteran of Outskirts (level).
Once everything in the room except you (and hopefully a Marine or two) is dead you should walk up the ramps to the top of the room. On the platform outside there is an unggoy and a Fuel rod gun, good for later. An elevator thing will show up with some foolish Kig-yar inside. Plasma grenade time! (Or instead if you don't have a plasma grenade or want to conserve some, a glitch allows you to shoot through the window on top of the elevator, so use your carbine or battle rifle to headshot the Kig-yar inside) Once the elevator is clear (or strewn with Kig-yar corpses, as the case may be), drop the shotgun in favor of a battle rifle, then step on in. We're going down.
You wind up in an underwater room with a pack of Unggoy running around. Empty the battle rifle into them. Each of the two sides of this room are occupied by Kig-yar snipers galore, a Yanme'e swarm, and waves of Honor Guards from doors on the lower level. A team of Sangheili and Kig-yar will emerge on the upper level soon after you kill the snipers, and soon Mgalekgolo will arrive. Head up the right side of the battle (there is a very rare possibility that the Drones will not spawn if you head up the right) and keep going straight until the floor drops of into an area with two doors onto the floor. Run out the rightmost one and head for the exit. The Mgalekgolo will generally fail to notice you if you're fast enough. Indeed, they won't even notice you jumping over their heads sometimes. If you saved the Fuel rod gun from before you can use it to blast the Hunters.
If you really want to stick 'round and fight things out, I'd suggest saving beam rifle ammo whenever possible, using cover to its fullest, and being very, very careful. And don't expect that by sticking around you'll save your Marines: even when it looks like you've won, the Marines will manage to kill themselves in some inane and non-heroic manner. Go figure.
The next room has two invisible Elites and four invisible Grunts. They shouldn't be too difficult for you to snipe with the beam rifle. When they all die, a stealth Elite with an energy sword will show up at the far end of the room. Shoot him down and drop the battle rifle; from here on, we'll take our chances with the energy sword.
Whew. Moving on, enter the elevator and head on the next leg of your journey. At the end of the ride is a foolish Honor Guard patrolling in the other direction. Bop him in the back and kill him dead. Another Honor Guard, this one with a plasma rifle, leads a Lance down the next hall, so take them out with sword and grenades. Next, we'll be back outside, facing four Drones, three or four Jackals and two Elites. Be sure to snipe the Drones first. I don't know why, but the Elites and Jackals will often retreat once the Drones fall. At that point, take out anybody still visible with the sniper before moving in with the sword and chopping them up.
Again, the Pelican will show up once you're done. One wonders why, again, he doesn't just pick you up and drop you off at your destination, which can be barely five hundred meters away. At any rate, he'll drop you some more Marines and weapons. Hand off your beam rifle to one of the Marines; that should leave one Marine with a shotgun, which will be fairly handy for him in the next area. Grab a sniper rifle. This next area is more or less the last conventional battle in the level; after this, we have an encounter with a sniper, a defense against some Banshees, a battle against a Grunt AP team and some Ranger Elites, an assault on an entrenched position, and a constant tango with Honor Guards as we fight a boss battle. So, enjoy normal combat while it lasts.
As you move into this area, a Jackal sniper will be ahead of you. Stick him with a grenade and drop off the path to the left. As you move around the left, a Grunt will show up in front of you; beat him down with the rifle. Jump up onto the ledge, take a right, and then drop back into the main battle, where two Jackal snipers and an Elite will be trying to focus on your Marines. Disrupt their concentration with the sword. Actually, the shotgunner will often take out the Elite if you handle the snipers.
Once the Covenant here are dead, your Marines will hopefully have survived. Jump out of the pit area and up onto the big rock facing the lake. A Phantom will soon arrive from that direction. The rock provides barely adequate cover from it. As it moves over the pit area, you'll see it drop a trio of Jackals. Leap up and lob a frag grenade into the spot where they land; with luck, they'll never hit the ground. A trio of Grunts will follow. Give them the same treatment, then drop off the rock and head for the hills, as your shield has taken a beating from the Phantom by this point.
Drop into the pit, bust out the sword, and use it to finish the two Elites that dropped from the Phantom while you were getting over here. Then jump up onto the fallen pillar to your left. There will be a space through which you can jump to get to the next area. The Marines can't follow you through here, but that only means they have to take the long way around, giving you some stealth time. There's a Jackal sniper hidden among the crates here, but the sword will end his reign of terror.
Whew. On to our last gondola. This gondola is the site of two and a half battles, and they're all fairly tricky, so stock up on guns. Get all the shotguns, energy swords, plasma pistols, sniper rifles, rocket launchers, beam rifles, battle rifles and carbines that you can find onto the gondola. Then, give your Marines sniper weapons (preferably ones low on ammo, so you don't have to use them), grab the rocket launcher instead of your sword, and take off. Almost immediately, two Banshees will show up behind the gondola. As they are so lethally damage-dealing, you'll want a bit of cover to unleash the awesome power of the tracking rocket on them. Two rockets each should do the trick.
Soon, the other gondola will show up, heading the other way. There are two ranger Elites and four Grunts here. Two of the Grunts have fuel rod guns, so I'd suggest boarding the other gondola, using the rocket launcher's remaining ammo to clear a path, and close with the fuel rod guns Grunts before they can deal much damage. If you did this in vidmaster-perfect style, you should have gotten one or both Rangers confused enough that they're just sitting and staring at nothing—easy targets for a skilled sniper like yourself.
If you're feeling a little OCD about firepower, you could grab the fuel rod guns in exchange for your spent rocket launcher, but I doubt you'll need it. Once everything on the far gondola is dead, hop back on to your own and continue. You have but two battles left on your arduous journey. The next one is actually remarkably pleasant, but the one after that is boring, difficult, drawn-out and contrived.
As you approach the temple, you should probably get rid of the rocket launcher, empty or not, and pick up a carbine or battle rifle—whichever you have more ammo for. There are a couple of Grunts mounting a defense outside the temple. Slaughter them, and they'll panic and run. However, they will soon return, having enlisted the aid of two Elites, two turret Grunts, and two Jackals. Use this battle well, as the fun is pretty much over for now.
03: Sorry, Were You In The Middle of Something?
Actually, Regret doesn't seem to be in the middle of something. One could question why he's actually here. Other than to give us an unreasonable and irritating boss fight, of course.
Head inside, swapping out your beam rifle or sniper rifle for a plasma pistol; it's 'noob' combo for great justice here. As you do, watch out for the bottom level; two Elites will spawn there, but should fall to the 'noobish' might of your overcharge and headshot. Once they fall, the door on the top level will open and reveal a Grunt or two and a pair of Honor Guards, swords in hand.
Kill them with the 'noob' combo as needed.
Here, I'll insert the valuable (and wonderfully entertaining) notes of Mike Miller on this fight: "At first glance, it seems that the Prophet plagues us with the very same elements of video-game-boss cheesiness as the heretic leader (for all the good that it did him):
Regret is pretty tough, but pretty stupid. His general strategy is to whine at you in his irritating voice, fire a lethal blast from his gravity beam cannon whenever you stand still too long, and teleport from one side of the room to the other every so often. You have to press X to board his chair, then B five times in a row to smack his face around. You need to deliver twenty-five punches to kill him, which is a bit tricky, especially given the fact that infinite quantities of enemies will try to stop you and he himself will teleport away every five hits (or five seconds).
Note: You can kill the Prophet of Regret in one go if you manage to board his throne and just manage to land a sixth punch right before he teleports away. You only have to board his throne once if done correctly. This has worked on a few occasions.
Interestingly, this is not the fastest (or only) way to kill Regret. Robert D. Perez has shown those of us with good trigger fingers a quicker way. Note that this is the only way to kill Regret when the Mythic Skull is active (he is talking about Mythic here): "I’ve jumped (boarded) on the Prophet of Regret’s throne exactly 48 times, say again 48 TIMES!! And each jump consists of five melee attacks. All to no avail. The bastard still lives! It was hopelessly disappointing and painfully frustrating to go back to square one after ALL those efforts. Then I simply thought of something out of this inevitability; what would the Master Chief do in a circumstance such as the one I’m overwhelmed in. Surely there has got to be another way, instead of the 48 plus jumps and five melee attacks per jump. I collected my thoughts and recounted the options I had, had another hard look at the weapons at my disposal.
It then hit me! Nothing can penetrate his immensely resilient force field. Other than the fact that once you jump on him you have the advantage of striking him with your melee attacks. So what to do? Well, it is quite simple; you throw a Plasma Grenade or a Fragmentation Grenade on him a split second before you board his throne. Picture it like this, your throwing arm penetrating his force field before you throw the grenades, with this objective the grenades will land or stay inside his force field. Therefore it is important that you throw the grenades inside his force field before you are unable to do so when you board. Remember that our Master Chief cannot throw or use his weapons when he has actually boarded the throne. Adversely if you throw them too early they will not stick or stay inside the force field. Or as in the fragmentation grenades case they’ll simply rebound off his force field, thus musing the already contempt Prophet of Regret. At other times, if you are unlucky the plasma grenades will also bounce, though feebly off his force field and may end up adhering to you instead, a big no-no to avoid. So you MUST throw the grenades a split second before you latch onto his throne and not a moment too soon.
If done correctly the Plasma/Fragmentation Grenades will drop inside his force field and not fall off. The resulting explosion will then knock him hard, so for added effectiveness commence punching him straight afterward or before the explosion (you’ll only land in two or three punches, as shortly afterward he’ll teleport in a fragile panic).
Don’t worry about getting killed or damaged by the plasma grenade since the explosion occurs inside of his force field. It will not harm our Master Chief. Just be sure to throw the grenade before you press and hold on to the ‘X’ button with which to board his throne. If he is at a higher elevation than you are at, then all you need to do is press the 'A' button, throw the grenade and then board him. This is simply a brilliant tactic on Bungie’s forward thinking. You will need to do this about six times to finish him off entirely or maybe more if your grenades do not fall inside his force field. Use your EARS to listen and to home in on the direction he’ll spawn to next. It’ll guarantee and reward your efforts with a far better success rate. Your radar is your best friend in these given circumstances, as the battles to follow are hectic to outwit.
You can also drop the grenades inside his force field without boarding his throne. Run up very close to The Prophet of Regret’s throne and throw your grenades at point blank. If done successfully the grenades will drop inside his force field. Please note that this method will not yield the desired effects on every attempt as it is at times hard to judge how close you are to the Prophet of Regret. Amidst all the battle commotion and pandemonium it is especially harder to pull off.
Lastly, don’t forget to PATIENTLY take out the re-spawning Honor Guards as well as the Grunts who’ll make certain of your efforts being anything but a success. Take them out before engaging the Prophet of Regret. The best way of doing this is to run back up the side ramps and look out for them on the top level. Check your radar as well if you cannot see them from this higher elevated vantage point. And lastly don’t forget to MOVE! Otherwise the pesky but cute little grunts will find you an easy target for plasma grenade shelling."
And for those of use with slightly "less machine-like timing than Robert D. Perez", Sid Fleischmann has posted another possible tactic.
Indeed, both strategies work, and are far quicker than the normal way. However, since both require a decent amount of luck, it is generally safest to use the 'noobish' but deadly strategy I've outlined above.
Another strategy you could use involves the rocket launcher. When you get into his throne room, make sure you have at least two rockets left. Go in, lock on to his chair from the ledge in front of the entrance, and fire the rockets. After both rockets have hit their target, jump onto his chair and punch him to death. It will only take about two punches to kill him.
Once your enemy finally goes down, watch the pretty cinematic. Congratulations are in order.