Thorim ( tactics ) Thorim is one of the watchers boss encounters in Ulduar . The encounter has two phases , in the first , the raid has to split in a gauntlet and an arena team . The arena team must fight waves of adds while the gauntlet team makes its way through some trash and a few mini - bosses to Thorim . Upon reaching the boss , he and the gauntlet group join the arena team , starting the second phase which lasts until Thorim is subdued . Both , fire and nature resistance are useful . When attempting hard mode , a little frost resistance gear is recommended . Adds . Initial mobs . These mobs aren ' t much of a threat - killing the healer ( Acolyte ) first is a good idea though . Phase 1 . The fight is started by killing the trash mobs in the Arena ( healer first ) . Thorim casts Sheath of Lightning on himself , making him almost invulnerable . After the mobs are down , the lever next to the gate on the left becomes active . The raid should now split in two , one part goes down the hallway to reach Thorim , and the other part stays in the arena to fight waves of adds . The Gauntlet . The gauntlet team needs one tank and one healer . In 10 player mode , 1 - 3 damage dealers suffice , in 25 player mode an extra healer and about 7 damage dealers should be sent . Ranged DPS is better suited for the gauntlet , mages in particular . The gauntlet team must move quickly , because after 5 minutes Thorim wipes the raid . There are 3 groups of 3 Warbringers . They can be Crowd Control led , ( Polymorph in particular ) . Two mobs should be CC ' d while the others are killed . At the end of the hallway is a large golem . In regular intervals it raises one arm and does damage to anyone on that side of the hallway , much like Skadi . A short time after it is engaged it gains a buff which decreases damage taken by 50 % , so if using cooldowns it ' s best to use them early . After defeating the golem , the door behind it opens and mobs start spawning on top of the stairs . Defeat or CC the two sets of two mobs already standing there and quickly run up . When the giant aggros , he buffs any adds still alive , but the adds stop spawning . The healers must have LOS to the tank but stand outside the giant ' s stomp . When the giant is positioned at the top of the stairs , the healer can stand about halfway down . After the giant is defeated the gauntlet team runs towards Thorim and jumps down into the arena . Someone must use any ability on Thorim to make him join . While running the large circles on the ground must be avoided , they are traps which briefly stun players standing on them . Arena . Those raid members which are positioned closest to Thorim gain initial aggro from all adds wich spawn . A simple setup for the arena team is to stack up dead center in the room . This avoids getting hit by the charged orbs , and also greatly increases the effects of both , AoE healing and AoE damage . The disadvantage of this method is that it makes the raid more susceptible to Stormhammer - it ' s possible to just take Stormhammer , but the group can also try to quickly spread out when it hits . The most dangerous mobs are the Dark Rune Champions which do a whirlwind atteck . They need to be kept away from the main raid , and / or disarmed . The Evokers casts heals - over - time that heal for massive amounts and also cast magic damage shield that can be stolen by mages . Both are dispellable and need to be dispelled / stolen quickly . Wound poison helps to reduce the amount healed . Phase 2 . Once Thorim is activated , he jumps down into the Arena . The mob waves stop spawning . During the whole of Phase 2 , Thorim gains an extra Lightning Charged buff every 10 seconds . This buff stack progressively increases damage and attack speed , it ' s in effect a passive enrage timer . From about 7 stacks on , healers and tanks need to use some CDs to survive , after about 15 buffs Thorim ' s melee hits can one - shot even the best geared tank . After Thorim is in the arena , he needs to be picked up by the MT immediately . The raid should spread out to avoid extra damage from Thorims ' chain lightning . Every time Thorim uses Unbalancing strike ( which is every 15 - 20 seconds ) , tanks need to taunt him off each other . When Thorim uses Lightning Charge , small lightning balls come from a column . After a short time , that column deals large amounts of AoE damage in a 60 degrees angle , this damage may be enough to one - shot players after the third Lightning Charge . Hard mode : Lose your Illusion . If the gauntlet team reaches Thorim within 2 : 45 min ( 6 : 15 on Heroic ) of killing the adds in the entrance , the illusion of Thorim ' s wife Sif joins the fight . Additionally , Thorim gets + 43 % health and + 67 % damage compared to Normal Mode ( it is not only + 30 % / + 40 % , since the debuff Touch of Dominion being applied for Normal Mode reduces his stats by - 30 % / - 40 % from the Hard Mode values ) . While the increased damage is not a large deal , the additional HP make the fight longer , which means a substantially higher stack of Lightning Charged . In hard mode , Thorim ' s Chain lightning is very dangerous to melee , so it is advisable to form 2 - 3 melee camps more than 8 yards from each other around the boss , as with Kel ' Thuzad at 60 . Sif herself is unattackable . She has four abilities which when chained together can kill raid members very quickly . When Thorim is defeated ' Sif ' reveals itself for what it is : an influence tentacle of Yogg - Saron . Tips . Demoralizing Shout cuts the damage the tank receives from unbalancing strike by 40 % . Shadow priests can MC a Dark Rune Warbringer . Besides dealing high damage , they also give all nearby allies a permanent buff called " Aura of Celerity " , increasing melee , ranged and spell haste by 20 % , practically a permanent Bloodlust ( also requirement for the achievement / ) . When mind controlled , these mobs also do more DPS than most player characters . Quotes . Sound files . See " Sound Files of Ulduar : Thorim " Related achievements . Hard mode . The following achievements are for the encounter ' s hard mode :