As the description says you have to complete Act 1 Chapter 6 (Standard or Arcade) on any difficulty, I got mine on Normal.
This chapter starts right after you get out of the elevator and slide down the wire with the hook. As soon as you land take cover and there will be a bunch of enemies waiting for you. After you kill them, you’ll move forward and will find some kind of locust station. There will be two Troika Turrets (machine gun), try to take one over so you can kill the rest easily.
Once inside, move through the left side, until you find a closed room. Take the stairs and once up follow the road all the way until they ask you to choose a path. It doesn’t really matter which one you choose but I took the Catwalk.
Go straight, then take a right and take the stairs. Clear the area and you will open some gate. After a cut scene you will start walking and have some tickers on your way, kill them and you’ll have a checkpoint. As you keep walking, they will start to shoot you with Mortars (balls of fire from the sky). Take cover in the containers as you keep walking to kill whoever is shooting you with the Mortars. After that you’ll have a checkpoint.
A Gas Barge will appear from the sky that looks like a Hot air balloon. Take one of the mortars from the enemies that you just killed and shoot the Gas Barge.
After that you will walk in a small dark road with several enemies. Keep forward until the end of the road and turn right, climb the ladder, and once up move slowly. There you’ll fight a bunch of locusts from all kinds. Try to take down first the more dangerous ones: Troika Turrets, Snipers, etc.
Then you will have to drop the Tickers onto the Lambent Leviathan. Just get close to the container and Press X, and Achievement Unlocked, you’re done.
I think this chapter was fun and fair, I’m sure you will not have trouble getting the achievement.
Best of luck.