Look Out for the Little Guys Achievement in Halo: The Master Chief Collection

During this mission, there will be a fair amount of Grunts that will get in your way when attempting to reach your three main objectives. Since the Flood and the Covenant will be frequently fighting during the mission, try to sit back and wait out the firefight. The Flood will almost always kill the Covenant, thus reducing the amount of work necessary in trying to slip by enemy Grunts without killing them. In addition to this, the majority of the Grunts only appear during the first half of this mission.

If you are playing with a Co-Op partner, you can always try staying back and having your partner clear the rooms and areas with Grunts before moving forward towards the objectives. This makes things a little easier, though you will have to replay the mission twice for both players to unlock the achievement. Once the final pulse generator has been disabled, the achievement will unlock providing you haven’t killed a single Grunt.