Devourer Slayer Achievement Guide
There are actually two ways to do this achievement. The first way is the most profitable, easiest (not in terms of difficulty but in terms of completing the achievement quickly) and most fun way to complete this achievement. The second is still kinda profitable, extremely easy to do (in terms of difficulty) but will take mountains of time longer than the first method. So, the first method is simple. What you will be doing is running Citadel of Flame (CoF) Path 2.
During this run there is a part of the dungeon that has you kill tons of Devourers. I don't know exactly how many but it is definitely enough to make this achievement move along quickly. If you are not too concerned with getting Devourer Slayer quickly I recommend running CoF path 1 and 2 daily (mainly just for money) which will eventually net you this achievement. You will also work towards your Flame Legion slayer achievement and aside from that you'll make amazing money farming here.
The second method is pretty much farming Devourers out in the open world. There are a few different locations you can do this but the best one that I have found is the Devourers in northeastern Blazeridge Steppes. They can be found just southeast of Terra Carorunda Waypoint. The reason I chose this location is because the Devourers here are extremely easy to kill, can be rounded up and AoE'd down very easily and they also drop Scales and Smooth Scales.
Scales and Smooth Scales are two extremely valuable fine crafting materials since they both are used in crafting Vitality gear which is some of the best gear for people who are leveling alts up. As you may know from my other Slayer Achievement Guides I tend to choose locations that will give you a good balance between making a lot of money and getting done the Slayer Achievement quickly and I can honestly say that no location is a better balance between the two than here.
Below is a picture of where you can find these Devourers on the map.
Another thing I need to mention about this area is it is home to some of the most valuable gatherables in the entire game. You will find Iron Ore, Gold Ore and Seasoned Wood Logs commonly in this area, all of which usually sell better than any other gatherable in the entire game. Those are just the common gatherables you will find, the more rare ones are Mature Herbs which there are usually three spawns up at any given time in this area. These herbs have a chance of giving you things like Chilli Peppers, Dill Sprigs, Mint Leaves and other goodies.
Chilli Peppers sell for extremely high amounts, but Dill Sprigs sell for even more than Chilli Peppers being the only Chef gatherable to break 10s each. That's pretty much all you need to know about this location, everything else is just you farming the Devourers for your Slayer Achievement. Although, if you're interested in learning more about the gatherables here I strongly recommend you check out my Blazeridge Steppes Quick Gathering Location.
In closing, below is a video I made of this location explaining pretty much everything I explained in this guide, just without all that pesky reading ;D