One Final Firefight Achievement in Halo: The Master Chief Collection

This achievement is best earned on the Easy difficulty with every skull, minus Blind and Mythic, activated.

The strategies involved in completing this haunting task all boil down to one aspect: stay alive and kill everything. By attempting this on Easy with so many skull modifiers activated at once, it will, in turn, lower the base difficulty while still providing a decent bonus multiplier. Make no mistake, however: this will still be pretty difficult and even a single uninterrupted, successful run can take anywhere from 50-60 minutes.

With that said, the actual core strategy here involves using the DMR to headshot Grunts and performing melee attacks/kills on the Elites (to both kill them and regenerate your shields). After some time doing this—typically 5 minutes—Elite Generals will begin to enter the battlefield (these are the heavily armored golden Elites). You'll want to snatch an Energy Sword after killing one of these Generals and then use it for the rest of the mission (obviously switching it out as necessary when ammo is depleted). The best area to bunker down at this point is right below the starting point; you will usually only be mobbed by 3-4 Elites at once.

From then on, the firefight will become a tedious battle of melee attacks against the Covenant. As mentioned, it will likely take upward of about 60 minutes, maybe even more, to net the required score, but, once you do earn 150,000 points, you can get yourself deliberately killed to end the mission and unlock the achievement.