Cold as Ice Achievement in Halo: The Master Chief Collection

On this map, new environmental stalactites have been placed above certain areas of the battlefield as a means of breaking up firefights with alternate means. The first stalactite is located above the Battle Rifle tower, another is located above the top-center platform, and the last stalactite is located just above the ramp behind the Sniper Rifle tower. For this achievement, it's best to start a Custom Game with another player and have them stand underneath the hanging ice. Now shoot the stalactites and it will break and fall, killing your partner and thus unlocking the achievement almost immediately.