Seeing as I couldn't find anything moderately current and relevant, I decided to make this.
In any case, nowadays it's nigh impossible to get this achievement, since you need at least one other player from the opposite faction around to get the achievement, and on top of that quite a few other npc's to be the one to spawn from a pool of a freaking lot of irrelevant ones. For anyone and everyone that're still in need of this achievement, or are just willing to help others get it, Feel free to say so here, aswell as region and realm! Let's help each other out here, for the good of all would-be Flamebreakers!
As of posting this, I've got Thassarian, on EU Doomhammer/Argent Dawn.