That Just Happened Achievement in Halo: The Master Chief Collection

While this achievement seems tough, it’s actually quite simple so long as you choose effective weaponry to use against the Flood and avoid the Carrier Forms at all costs. As a recommendation, try to pick up a Shotgun and Needler during the first few firefights. The former weapon is perfect for taking on the Flood in close-quarters while the latter is useful when at a ranged distance. In addition to this, if the Bandana skull is activated for this mission, the unlimited ammo and grenades will prove to be extremely beneficial.

Progress through the level and make sure to avoid the Carrier Forms. Once they get close, they will fall onto the ground and explode. These explosions will often time kill you if your shields or health are low. Other than that, there are also two instances where Combat Forms are wielding Rocket Launchers, so be careful not to be caught in their line of fire. Once the final cutscene concludes, the achievement will unlock providing you did not die at all during the mission.