During the Thorim fight, your raid will separate into two groups. Make sure you have two tanks! One will go off into the hallway after you kill the initial adds. Keep your best DPS out in the arena. The hallway group will kill some adds before reaching the Ancient Rune Giant. The Rune Giant will shoot fire out of his arms that will extend down one side of the hallway. If you are standing on the same side as the fire, you will die. So assign someone to call out which side of the hallway to run to. This mini boss goes down easy. After him, the hallway group will move on to kill some more adds before hitting the Rune Colossus. This is also a simple mini boss, however, he casts a spell on one person in the group that will cause them to become immobile. After the debuff wears off it will cause AOE fire damage, so make sure everyone runs away from that person. As for the group in the arena, they will be hit by waves of mobs. You will definitely need a good AOE tank. Make sure your healers (if you are running with 3, it's best to keep two outside in the arena) stand on opposite sides of the circle. Throim will cast Stormhammer quite often and if one healer is stunned while the other has increased cast speed, you will run into problems. Here are the kill order of the adds: Dark Rune Champions first (they are the biggest adds), Dark Rune Warbringers, Dark Rune Evokers and Dark Rune Commoners. They won't necessarily all be in the same group, so make sure you pay attention. After your hallway group kills the Rune Colossus, Thorim will join the fight. Make sure that group gets down as fast as possible, or they will die. You'll need both tanks for this phase as Thorim will cast Unbalancing Strike. As soon as your tank gets this debuff, he/she needs to call out a switch. Another thing the raid needs to watch out for is Lightning Charge. You will see a chain of lightning coming from Thorim and extending to one of the orbs in the room. Make sure all raid members move out of this chain as Thorim will turn to that side and shoot lightning! Thorim goes down easily, and you will earn this achievement just as easily.