Dark Alliance

This one is definitely the worst of these “archetype” achievements solely due to how buggy it is. I had to create a brand new character for this one to unlock.

There are a total of five different archetypes of Trolls: Red, Green, Acid (the one with bubbles all over him), Frost, and Electric.

Keep in mind that we need to kill the elite versions of these enemies. Elite enemies have the skull icons by their health bar and a green glow over their bodies.

Red
The red troll can be found in the mission, “The Broken City.” Near the beginning of the level you’ll come across a big purple bubble protecting a runestone. There’ll be four trolls that pop out and by killing them will spawn the elite variant of the red troll.

Green
The green troll can be found in the mission, “The Floating City.” From the start you’ll want to follow the mission arrow until you get to the runesword being protected by a purple bubble. You’ll then want to make a left and take the portal. Keep heading forward past the acid plants and then you’ll be in an open area where you’ll see the green elite troll come out of the ground.

Acid
For this one you’re going to load up the mission, “Designs of the Duergar.” You’re going to want to head towards the end of the mission for this troll. When you open the gate after pulling the lever, you’ll gain access to a fairly big area. You’ll want to head straight until you come across a named enemy called, Gruuln Threechin. You’re going to want to run past him and make a left, jumping up on top of the two ledges. Once you jump up, you’ll then be presented with the acid elite troll.

Frost
This troll is located on the mission, “Ghosts of the Past.” Right at the beginning of the level you’ll want to head straight running past the first group of enemies. As soon as you go downhill and make that right turn you’ll notice a ladder on your right-hand side. Climb up it and then take out those vines covering the chest. Open the chest, and you’ll notice The Collector come out of his hole. Be sure to take him out.

Electric
Thanks to @FayMoon, it appears that Stonegrinder is also required for this achievement. The final troll that we need can be found on the mission, “Halls of the Duergar.” Simply head all the way to the end of this mission, completing the objectives in order to gain access to the final boss of the mission. After you take him down, the achievement should be yours!

Advice:
-Avoid co-op when running through these missions as I believe they can bug out your achievement due to the fact that it doesn’t count the kill if you don’t get the finishing blow.

-Based off my experience, you’ll need to at least play on T4 difficulty for the elite variants to consistently spawn.

Hopefully after running through these missions you were able to unlock this super buggy achievement. If it didn’t unlock for you, I suggest running through these missions again on a brand new character.

Good luck everyone!