Hunted Demons Forge

Near the end of Chapter 5.2 (just before 5.3 entering the Sewer) is a good opportunity for this.

As E'lara, hopefully she has upgraded some of her weapon magic, namely Pyre Blast - Rank 2. There are a couple of Eyes of Annuvin roaming around with Wargar that don't notice you yet. Aim and time the ability just right and it should take it out in one shot. I found using Pyre Blast easier than shooting it with an arrow as I have a harder time leading shots with bows, the weapon magic seems to be quicker. This was on the Normal difficulty setting.

As Caddoc, the fully upgraded Dragon's Breath spell seem to work just as well (credit to DivineWind72 and Cellar Attic for the info).

Only the person taking the shot will get the achievement.

Not really a solution but an observation for those playing on harder difficulties. Eye of Annuvins have a resistance to Pyre Blast but an extreme vulnerability to Arctic Arrow. So if you are having a hard time getting it using Pyre Blast use Arctic Arrow rank 2 or higher instead.

During Chapter 5.2 there is a section where you need to cross a large open area and under a bridge. You will then need to make your way into the sewers on the other side of this area. Just before you leave the wooden ramp you walked down, carefully line up your shots withe explosive arrows or armor-piercing arrows and destroy one of the Annuvin eyes before it alerts the other enemies.

This may take a few attempts, but with the right level arrows and abilities you should kill one in a single shot.

Credit to http://leadexample.net/guides/retail-guides/hunted-the-demon...