The level takes place in Cauldron, and you start at one "end" of the level. Make your way to the first UNSC ammo crate and pick up a Battle rifle if you want one. Make your way through the cave and you'll see two Unggoy being watched by a Phantom. You now have two options to attack here:
1.You can stay on the bottom path and take out the Grunts quickly, although the Phantom will see you and take a few shots before leaving.
2. You can take the top path that leads to a vantage point over looking the main Covenant drop-zone, giving you superbly better view of your foes, but this puts you directly in-view of a Grunt using a plasma turret. Because of the Grunt's small size, it'll take several shots to destroy the turret and it will be impossible to headshot him.
Which ever way you pick, the Phantom leaves to alert the Covenant of your presence, and a drop pod with more reinforcements. The enemies in this area add up to about eight or so Grunts, five Kig-Yar, and three Sangheili. Hang back and let the Elites and Grunts charge you so they have to fight more on your terms and be forced to group together. On higher difficulties, the Elites are high ranking and one might even have a Fuel Rod Cannon. As you climb the ramp leading to the platform, two Phantoms will fly in behind you. They won't drop any Covenant, but they will take potshots at you as they fly away. After dealing with them, most of the Jackals will tend to stay back and stay on the top platform, so you'll be eliminating them last.
After you clear the area and hit a switch, another Phantom appears from the direction you're facing, and two Ranger Elites fly in, one of them definitely holding a Fuel Rod Cannon on Heroic or harder. Get rid of them before two more switches appear. Activate them both.
The door ahead opens, and a large number of Grunts bunched together and three Elites will file out. toss a grenade among the Grunt crowd, then take out the Elites as they charge. The last Elite has a Concussion Rifle, so save something extra for him. Upon entering where the came from, a steep ramp will lead to the last set of Covenant. Three Elites, with one holding a Fuel Rod Cannon, supported by four Jackals and a few Grunts. One is manning a plasma turret on the raised platform on the left. Phantoms again fly overhead to bombard, so take cover and take it slow. Take out the Elites first, then the turret and then the rest. Grab some ammo and pick up the plasma turret when you activate the next switch.
A large group of Prometheans will spawn to attack. In total, there are about thirty Crawlers, four Watchers, and four Knights. About ten the Crawlers will spawn in your immediate area and attack. However, the platform you are on gives you an easy advantage. The elevation forces the Crawlers to all move up the ramp leading up to you, and all you have to do is sit there and pick them off as they come. Since they'll only attacks in groups of two or three, it's even easier. The remaining Crawlers will hold back, two or three being snipers. Head back up to the massive slope you entered the area from and one of the large impediments as a stepping stone to leap to the top of the rails. This gives you an excellent spot to snipe the Watchers while you're well out of their range. Eliminate them before the spawn additional Crawlers or turrets.
When you head up through the caves, four Knights will appear. At least one is a Lancer. Usually at least two of them will spawn a Watcher. The remaining Crawlers are here as well. Eliminate them from the vantage point on the raised platform on your left when you enter, and grab a Scattershot from the rack and a ranged weapon (there's a Covenant ammo crate with two Carbines, or the UNSC ammo crate with an extra Assault rifle) before hitting the button.
A final group of about six Crawlers, two Knights, and at least one Watcher spawn on the platform opposite of you and attack. Stand at the top of one of the ramps and let all the Crawlers rush you. The Knights will hold back since they're both carrying close range weapons. Kill the Crawlers, kill the Watcher, and finally snipe the Knights. One of the Knights is a Battlewagon (the other is a regular) and both may try to leap at or charge you, respectively. Use the Scattershot to get them. Grab the artifact and you're done.
1.The Covenant enemies in the second section are most difficult because they are all concentrated in one area and have plenty of cover. Be patient when dealing with this group.
2. Grab Fuel Rod Cannons dropped by Elites and Grunts as a last resort weapon. Elites take two direct shots, Knights usually take around 3.
3. The Grunts and Jackals are likely to use plasma pistols effectively on Heroic or harder, with one taking out your shields with overcharged shot and the others finishing you off with rapid fire.
4. If the Knights become problematic to eliminate (since they can take almost a full clip of ranged weapon ammo), go back to the Covenant weapon crates and use a plasma pistol to eliminate it's shield, then aim for the exposed face.