This page covers a healer-focused strategy for Thorim in Ulduar in Wrath of the Lich King. While it's tailored for healers, other roles may also find the information useful. If you have any suggestions or feedback, you can leave a comment below or tweet @PrestonDvorak.

This guide has been updated and maintained based on my own experiences with the encounter, combat log information, and Dungeon Journal information. I'll continue to update it as-needed.

Stage One - Prove Your Worth

This stage begins the encounter and ends when a player reaches Thorim through the Hallway. During this stage, players split into two groups. One group traverses the Hallway, to the left as you enter the Arena, to reach Thorim, and the other stays in the Arena dealing with lesser enemies.

Hallway

• Once the initial set of lesser enemies is killed in the Arena, the lever near the gate activates. A player can right-click on the lever to open the gate to the hallway.
• Ancient Rune Giant
  • Stay more than 10-yards away to avoid Stomp. Players hit take light damage and are knocked back.
  • Stay more than 15-yards away from players Rooted by Rune Detonation to avoid chaining the damage dealt.
  • Greatly increases the damage dealt by, Attack Speed, casting speed, and maximum health of enemies within 50-yards with Runic Fortification.
• Dark Rune Acolyte
  • Interrupt Greater Heal to prevent the healing.
  • Purge Renew to remove the healing over time effect.
  • When possible, interrupt Holy Smite to prevent the light damage dealt to a random player.
• Iron Honor Guard
  • The tank will be dealing with extra light damage and the Stun effect from Shield Smash.
  • Don't stand in front to avoid Cleave.
  • Stay more than 5-yards away to avoid the reduced movement speed effect from Hamstring.
• Iron Ring Guard
  • The tank will be dealing with extra moderate damage and light damage over time from Impale.
    • Healing the affected player above 90% health removes the effect.
  • Stay more than 10-yards away to avoid Whirling Trip. Players hit take moderate damage and are Stunned.
• Runic Colossus
  • Don't stand in front to avoid Smash.
  • Stay more than 10-yards away to avoid Runic Smash.
  • Purge Runic Shield to remove the damage absorption effect and prevent the damage dealt to attacking players.
  • Deals light damage to random players and knocks them back with Charge.

Arena

• If there are no players in the Arena, enemies spawned there will walk down the Hallway instead.
• Dark Rune Acolyte
  • Interrupt Greater Heal to prevent the healing.
  • Purge Renew to remove the healing over time effect.
  • When possible, interrupt Holy Smite to prevent the light damage dealt to a random player.
• Dark Rune Champion
  • The tank will be dealing with Mortal Strike, reducing healing received.
  • Stay more than 8-yards away to avoid Whirlwind.
  • Deals light damage to and Stuns random players with Charge.
• Dark Rune Commoner
  • Stay more than 5-yards away to avoid the Interrupt from Pummel.
  • Targets random players with Low Blow, reducing damage dealt.
• Dark Rune Evoker
  • Interrupt or Runic Mending to prevent the healing over time effect.
  • Purge Runic Shield to remove the damage absorption and reduced Physical damage taken effect.
  • When possible, interrupt Runic Lightning to prevent the light damage dealt to a random player.
• Dark Rune Warbringer
  • The tanks will be dealing with extra moderate damage from Runic Strike.
  • Increases the Attack Speed and casting speed of all enemies within 40-yards with Aura of Celerity.

Stage Two - Keeper of Storms

This stage begins when Thorim is reached by a player via the Hallway and ends when he's killed.

• To begin the stage, Thorim jumps down into the Arena.
• The tanks will be dealing with extra moderate damage and the reduced Defense effect from Unbalancing Strike.
• Stay more than 10-yards away from as many players as possible to avoid chaining the moderate to heavy damage dealt by Chain Lightning.
• Every 15-seconds, during Lightning Charge:
  • Don't stand on the side of Thorim with the trail of small lightning bolts traveling out from it to avoid the eventual cone-shaped attacked.
  • Grants Thorim a stack of Lightning Charge, increasing melee damage dealt, attack speed, and Nature damage dealt.

To activate hardmode, a player must reach Thorim through the Hallway within 2-minutes and 45-seconds after the lever to open the Hallway gate becomes active.

• Sif joins the encounter during stage two.
  • Sif
    • Not attackable by players.
    • Stay more than 15-yards away to avoid Frost Nova (dispel, magic). Players hit take light damage and are Rooted.
    • Avoid the location of Blizzard as it moves around the room.
    • Every 15-30 seconds, deals light damage to and reduces the movement speed of all players with Frostbolt Volley (dispel, magic).
    • Deals light damage to random players with Frostbolt.

Quick Notes, All Difficulties

The notes below mostly pertain to progression difficulty, meaning if you out-gear the difficulty you're on or use extra healers they may not apply.

• Use Major Cooldowns
  • as-needed to keep tanks alive or if too many players are hit by Chain Lightning
  • (Hardmode) on Frostbolt Volley [occures every 15-30 seconds]
• Use Minor Cooldowns
  • as-needed to supplement Major Cooldowns when dealing with unexpected damage
• Pre-heal Before (mainly for heal over time classes)
  • (Hardmode) on Frostbolt Volley
• Other things to watch for
  • The tanks will be taking most of the damage during stage two if other players are spread out and avoiding mechanics.

Major

• Several abilities cause playes to need additional healing.
  • Impale
  • Mortal Strike
  • Rune Detonation
• Several abilites Stun affected players.
  • Whirling Trip
  • Shield Smash
  • Charge

Minor

• Frost Nova (dispel, magic) should be dispelled immediately.
• Frostbolt Volley (dispel, magic) can be dispelled immediately.

Buffs to Purge

• Renew
• Runic Shield
• Runic Shield
• Runic Mending