Thorim

Abilities

Charge Orb (Nature) - Will charge on of the orbs around the arena. Get away from the charged orb or you will take Nature Damage.
Stormhammer (Nature) - Throws the hammer at one target. Everyone near the impact will be stunned and take the following debuff:
Deafening Thunder (Nature) - You take Nature Damage and your casting will be slowed by 75% for 8 seconds.

Chain Lightning (Nature) - The chain lightning has no target limit and damage increases for 50% with each jump. Will be used in Phase 3.
Lightning Charge (Nature) - He will absorb lightning from a charged orb, gaining attack speed and damage increase. Get way from the electrial bolts on the ground. Will be used in Phase 3.
Unbalancing Strike (Physical) - Reduces the MT's defense skill by 200. Another tank should take over tanking. Will be used in Phase 3.

We will have additional enemies in the arena and on the gauntlet.

Gauntlet:

Dark Rune Acolyte:

Holy Smite (Holy) - Smites the tank.
Renew (Heal) - Heals a friendly target.
Greater Heal (Heal) - Heals a friendly target. Needs to be interrupted!

Iron Ring Guard:

Impale (Physical) - The tank will bleed until healed past 90% maximum health.
Whirling Trip (Physical) - Stuns the tank and nearby targets.

Iron Honor Guard:

Cleave (Physical) - Damages the tank and his nearest ally.
Hamstring (Physical) - Reduces the tank's movements speed by 60%.
Shield Smash (Physical) - Stuns the tank for 3 seconds.

Runic Colossus:

Charge (Physical) - Knocks back one enemy.
Smash (Physical) - Smashs all enemies in front of the caster.
Runic Barrier (Buff) - The Colossus takes 50% less damage and all melee attackers take Arcane Damage on strike.

Ancient Rune Giant:

Stomp (Physical) - Stomps on nearby enemies knocking them back.
Rune Detonation (Fire) - Roots a target and after 4 seconds he will explode, hurting everyone around him.

Arena:

Dark Rune Champion:

Whirlwind (Physical) - Whirlwinds nearby enemies.
Mortal Strike (Physical) - Reduces healing taken by 50% on the tank.
Charge (Physical) - Charges an enemy and stuns him for 2 seconds.

Dark Rune Commoner:

Low Blow (Physical) - Reduces damage dealt by 3% each stack. Stacks up to 25 times.
Pummel (Physical) - Interrupts spell casting for 5 seconds.

Dark Rune Evoker:

Runic Lightning (Nature) - Strikes a random target with Nature Damage.
Runic Mending (Heal) - Heals an enemy and places a HoT on him. The HoT can be dispelled and spell stolen.
Runic Shield (Buff) - Surrounds the caster with a shield for one minute, reducing his physical damage taken by 50% and absorbing 120k magical damage. Can be dispelled and spell stolen.

Dark Rune Warbringer:

Runic Strike (Nature) - Strikes the tank with Nature Damage.
Aura of Celerity (Buff) - Increases melee, ranged and casting speed by 20% for all friendly units.

Class requirements

Having three tanks (one gauntlet, two arena) makes life easier in the arena. Also having 15 dps helps as well.

The pull

The raid will run into the arena and clear the place of every mob.

Positions and strategy

After the arena has been cleared of the mobs fighting against the big worm, the group will split up into 2 teams. One team will have to do a gauntlet run through the door to the north. The other team will remain in the arena and fight off enemies jumping in from the ranks, trying to survive until the gauntlet team managed to reach Thorim.

Arena:

Fighting in the arena is pretty straight foward. The team will position themselves in the middle, having the dps and healers on the outer line of the inner circle. You will have to look out for Thorim's Stormhammer that he'll throw at random people. If you get targeted, you should move away for a bit to not hit all your comrades. Also staying in the middle makes you survive the Charged Orbs more easily.

When the adds start jumping in, you will focus on taking down the Evokers first as those are the healers in the arena. After them it's AoE'ing or single target. That depends on your tanks and dps available. You will continue fighting this way until the gauntlet team manages to reach Thorim thus bringing the fight into Phase 3.

Gauntlet:

You will need at least one tank, 2 healers and a bunch of range dps for the gauntlet. It's difficult to find the right balance between having too few dps in the arena or having too few dps on the gauntlet. Also you need to take mostly range dps, as the gauntlet doesn't favour melee dps.

After you run down the door you will enter a hallway with 2 trash packs and the Runic Colossus standing at the end. It will occasionally attack either the left or the right side of the hallway with a devastating attack. You will notice which side if you watch what arm he's holding up. Move to the opposite side to evade the attack.

The Acolytes need to be taken down first, as again, those are the healers on the gauntlet run. You can either CC the guards or tank them and AoE them down. Due to their AoE stun, they are difficult to handle as a tank and you will take additional damage when you can't avoid any attacks.

When you engage the Runic Colossus you need to watch out for his Runic Barrier, as that attack will make melee dps take additional Arcane Damage on attack.

Behind the door you will engage another 2 packs of trash standing close together. You take out the Acolytes and CC the guards and then run off to the Ancient Rune Giant and engage him to stop the adds of spawning behind him.

You need to spread out slightly to avoid getting killed by your comrades bomb. Once he's down you will kill the remaining adds, and run through the door to Thorim. Reaching him will make him jump down into the arena and starting Phase 3.

Phase 3:

The tank from the gauntlet team will start tanking Thorim while the raid will take out the remaining adds and then spread out in the arena to not get hit by his Chain Lightning.

Whenever he gains a Charge from the Orbs, raiders need to get away from the lightning bolts on the ground between the Orb and Thorim.

Also Thorim will use a devastating attack on the MT, reducing his defense skill by 200. At that point, a second tank needs to take over.

With every Charge Thorim gains in power, if you take too long, you can't keep up with his damage anymore.

Normal Difficulty

No difference in the tactic.

Boss Kill: