Leave It Where It Lay Achievement in Halo: The Master Chief Collection

At the start of this mission, you will be equipped with a Plasma Pistol and Shotgun. In order to obtain this achievement, you cannot switch out either weapon at any point in the mission. Fortunately, these weapons are rather useful against the both the Covenant and the Flood, and since both factions will often time battle one another, this reduces the ammo you need to expend on the enemy.

Attempting this achievement with a Co-Op partner is recommended as one player can swap out their starting weapons for more something more effective like a Rocket Launcher or Needler. In addition to this, if one player dies, they will respawn with an Assault Rifle, though this does not void the achievement. Once the final pulse generator has been disabled, the achievement will unlock providing you haven’t swapped out either of your weapons during the mission.