Seeing as there is no guide here, I'm referring back to my guide that I posted under the original Halo: CE Anniversary achievement with the same name.
Guide is as follows;
There are three area's in this level, the first two have missable Elites:
-The first section on the Covenant Cruiser (Elites are missable)
-The cooling liquid pools area on the ground (Elites are missable)
Everything after the Grav Lift is not missable. Follow a few steps below and you should be alright:
- Use the Bandana skull for infinite grenades and sniper rounds (you will get the sniper just before the grav lift, it will help kill spec-ops Elites quicker. Specifically the Sniper is on the last bend before the opening to the Grav Lift area. You would be extremely unlucky if you managed to miss this)
- If Elite's die before you get a chance to kill them, it counts as one of your kills.
- The two Elites at the start on the Covenant ship (on the opposite side of the large hole you fall through) count towards this achievement.
-Spec-Op Elites infinitely respawn in the Banshee hangar bay. They also hide. Cover all the floors and all rooms from top to bottom, then bottom to top and a third time on the way down to be sure. I have found 2 or 3 Spec-Op's in hiding when doing this. This will also stop the infinite respawn of the Spec-Op Elite's in the Banshee Hangar.
Unfortunately I no longer have a capture card so am unable to record this for everyone but as a rule of thumb, extensively cover the first section when you are on the Covenant Cruiser and also when you fall into the cooling liquid pools on the ground of the level. Every other Elite will be easy pickings apart from the first two areas.