Halo: Combat Evolved Anniversary

Stick in a second controller and play the level through with that, or play with a co-op partner. If your account is doing nothing at all, there's not much chance of it killing Grunts! You will want to periodically suicide with your account in the outdoor areas to prevent the account you're playing on being respawned miles back.

Credit to Master RC for this video.

This is a fantastic example of how to do this achievement solo without relying on the co-op method. I used it to get the achievement and it helped me immensely.

As Quickdraw pointed out, it's entirely possible to do this solo, and for anyone who wants to earn the achievement without using a dummy controller, I say go for it!

Ok this one is not so bad, but at the beginning its a real pain as you only fight covenant, you may kill elites or jackals but you cannot kill a single grunt. i also took out banshees where i could to ease taking damage.

If you can get a partner it might be easier, ok once you get control take out the drones then make your way out when you do there's several grunts and drones fight try and run past them and head out. Once you open the next door outside head left and stick to the cliff wall and the building, you can slide down without taking any damage once your at the bottom there's a med pack.

Next stealing a banshee try line of sighting as much as you can towards the hole in the ground where part of the structure is from there come out and run to the banshee and take out. Next land on the platform avoiding running anything down as there is a grunt with a fuel arm up there.

Later on there's another part with just Covenant best way i found to do this is stick to the left as there's not a lot of grunts after that there's a hall with a elite and grunts with pillars use the pillars to Line of Sight them so they cant kill you.

once flood start showing it becomes so much easier, just beware of banshees they hurt and grunt fuel rods.

While there's nothing wrong with the other methods, I found this YouTube video by "Nak3dHalo" that shows how to get the banshee and get a chunk of the early grunts to spawn late, so that you can avoid them. It helped me quite a bit. Just don't make my mistake and accidentally splatter a grunt. Make sure to fly up sooner rather than later when you spawn the grunts.

Best done in co-op. TURN ON THE BANDANA SKULL, it makes life sooo much easier with infinite ammo. Just let your friend kill all the grunts; it will not void the achievement so long as YOU don't kill any. There are a lot of flood parts, so feel free to get the killing out of your system then. You can also do this achievement on legendary right away and get the achievement for not picking up any weapons, which is where the bandana skull really comes in handy.

In my video i show how to get a free banshee and make most of the enemies not spawn up and how to correct the glitch and i show if you did it wrong or not.