As everyone has said, you must complete a campaign mission with all playlist LASO skulls on. For me, not being experienced with LASO at all, I decided to go for Halo: CE, since I can't stand not having a HUD. Load up the level 343 Guilty Spark, which is the shortest level in CE and also one of the easiest.
Right off the bat, run left towards the health packs and around the hills and trees till you come to the log you're supposed to cross to gain entrance to the structure. This will skip the first encounter with the Covenant. Next you'll see all the Grunts and Jackals running out of the structure, just simply wait for them to all exit then sneak past them to the elevator. Now comes the tricky part: Once the elevator stops, it's completely random what the grunts will do when you toss a frag into the little entrance. I've had times where it didn't do anything, kill one grunt, they all run away, or it kills them all, so just be patient and save/quit if it doesn't go well. After entering, try to frag the remaining jackals and sneak in a melee hit to gain back your shield if it's low. When entering the next door, you'll see a whole horde of enemies, so just throw a sticky at a grunt to kill all of them (due to Grunt Funeral).
From this next section to the flood room, just run, run, run. Don't waste time with random enemies at all. Also, pro tip, melee the panicked marine to gain your shield back + pistol ammo. Once you gain entrance to the flood room, kill the flood with your assault rifle. There's plenty of ammo to spray and pray in the room. Once the elite flood break through the door, wait towards the back of the room until the most of them enter, then book it for the door. If you didn't get the health pack on the way in, grab that and run through the rest of the section until you get to elevator #2. Once you stop, climb the boxes to your right to get an Over-shield. YOU WILL NEED THIS OR THE REST OF THE LEVEL IS ALMOST IMPOSSIBLE. After grabbing the Over-shield, run run run until you get to the box with the health pack and shotgun. Switch out your pistol for the shotgun quickly and then proceed to book it to the bridge switch.
This is the hardest part of the level, so be prepared. Once you activate the switch, you'll have to wait for the first swarm of flood to come out of the tunnel. Kill as many as you can, or just run a loop around the sides of the upper level to chase them away from the tunnel. Once you try to make it back to elevator #1, more flood will swarm you. I got very lucky and melee'd + shotgun'd + ran/pushed past them. They are very unforgiving here and will not let you pass if they are in front of you. You can't melee fight them like elites, so try your best to shotgun a path for yourself and rush past them. Once you're back on elevator #1, you're in the home stretch. Grab the ammo and health pack to your left and wait for all the marines to circle you before leaving the structure. The final stretch just involves you running from the structure to the lit tower. Don't worry about any flood, just run, jump, and sidestep to avoid fire. Once you're at the lit tower, the fastest way to end the level is to kill the two sentinels. Find them, kill them with your shotgun (which should be fully loaded), and wait a couple seconds, avoiding any flood near you. Then the cut scene will commence and *ding* achievement unlocked.
This might be an oversimplified version, but hopefully with these little tricks, you can get this bear of an achievement. Keep in mind, auto-aim is off, so you'll need skill and precision to get headshots/kills. Any comments or thoughts would be great! I know this guide is long, but the detailed nature of it should help those struggling. Good luck!