Those Left Behind

Those Left Behind is an achievement in Halo: The Master Chief Collection. This achievement is obtained when a player completes Tayari Plaza with at least one Marine still alive.

Method
While the achievement can be completed on any difficulty, the Marines, in their weakened states at spawn, would have a higher chance of survival on Easy.

Since the second group of Marines (three Marines found in Sector 8) can be easily killed by the large group of Covenant which surround them, players should focus on protecting the first pair of Marines (two Marines in Sector 6), one of which calls out to Buck with “Trooper, over here!” These two Marines will follow the player, and can be tricked into getting stuck behind the first locked door.

The player should rush ahead, avoiding Buck’s dialogue with the Marine, and take charge with killing the first pack of Brutes. Use plasma pistol to take down their power armors, then finish them off with headshots from the M6C/SOCOM.

As the road bends, stay ahead of the Marines and prioritise killing the Grunts, especially the gunner on the plasma turret.

After passing the area with dead Elites and Brutes, first take down the Jackal on the deployable lookout tower, then the Grunts and Jackals under the tower.

Before unlocking the door leading into Sector 8, lead the two Marines back to where they are first found, and lead them into the building where there are dead Elites and Brutes (where Buck would wonder aloud, “What the hell happened here?”), lead them upstairs, and then jump back into the street. This would slow down the Marines slightly, giving ample time to return to the first door, unlock it, and move through without them.

Proceed the mission as usual. The achievement would be awarded after ending cinematic.