It takes a minimum of 2 hours to do it, so I recommend doing it when you have plenty of free time to avoid having to quit in the middle of the quest.
Here are some tips I gathered during my ordeal:
1. Hammer/FRC Brutes are nigh-invincible(hammers) so you're better off assassinating them to conserve ammo and grenades. Hammers are easy to handle. You just need to rush them(sounds suicidal eh?) and then sidestep when you're near so they lunge forward smashing the air and then you assassinate them while they recover. FRC Brutes...well they're annoying.
2. Regular Brutes can be taken down with charged plasma pistol shots and headshots. Easiest/fastest way to handle them. Invisible Brutes like to throw flares, so watch out for those.
3. Hunters are tough, but with some dualtage they can be taken out. Sniper/pistol/carbine their backs when someone else has them distracted.
4. Grunts and jackals need to be taken out with pistol headshots.
5. Drones are annoying as hell. In the first rounds they don't do much damage, but once they get shields and start wielding the brute plasma rifles...well they're tough.
General Tips:
1. Try Alpha Site since the map's design is like an x and covenant can only enter via 2 halls. So you can pretty much deal with them from the other side of the map.
2. Don't ever be in the middle. Its too risky with all the grenades they will be throwing.
3. Once the round ends gather as much ammo/weapons as you can. Rockets are outside the x so you should make it a priority to gather them before the covenant come shooting down the house.
4. Once you beat a set a bonus round will begin. All the skulls are activated and you dont get respawns. The covenant will land in the middle of the room and start throwing nades/shooting/etc. Make sure you greet them well.
5. This is obvious, but avoid death as much as possible because once you clear a set you get more lives and its a priority to stack as many lives as possible before the 4th set begins. We would've cleared it had we been more careful with our lives in the beginning.
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Good hunting.