Kologarn is a giant who guards the way to the central ring in Ulduar.  He must be defeated so that his body will form a bridge to reach across the Shattered Walkway so that you can gain access to the other bosses.  It is possible for Kologarn to be fought as early as the raids 3rd boss in Ulduar or as late as the 6th depending on which optional bosses your group chooses to fight.

Health

10 Person Raid: Body - 3,600,000 health, Arms – 545,000 health

25 Person Raid: Body - 15,340,000 heath, Arms – 2,300,000 health

Abilities

Focused Eyebeam – Kologarn can focus his gaze on a random player that is not in melee range of his main body and shoot energy beams at them.  The beams cause roughly 4,000 damage per second to the target and anyone else within 5 yards (3,000 damage per second in 10 player raids).  The beams will follow the player at slightly less than run speed.

Overhead Smash – Kologarn uses this high damage attack against the main tank.  It can also apply the “Crunch Armor” effect, which will lower the tanks armor by 20% for 6 seconds.  Kologarn generally uses this ability every 10 – 15 seconds, however it is possible for him to use it more often.

Petrifying Breath – Kologarn uses this attack anytime his main agro target is not in melee range.  It is a channeled spell that lasts for 4 seconds and does roughly 20,000 damage per second (15,000 in 10 player raids) and applies the stacking “Brittle Skin” effect. 

Brittle Skin – This is a debuff caused by Petrifying Breath and increases damage taken by 20% for 8 seconds.

Stone Grip –While Kologarn’s right arm is alive, it will grab random players to stone grip.  While in the arm’s grip, the player takes roughly 5,500 damage per second (3,500 damage per second in 10 player raids) until the player dies or is freed.  To free a player from the stone grip, DPS players must cause 450,000 damage (150,000 in 10 player raids) to the arm.

Shockwave – While Kologarn’s left arm is alive it will cause steady shockwaves that cause roughly 10,000 nature damage to everyone in the room.

Elementals – Whenever an arm is destroyed a pack of elementals will spawn from the rubble.  The elementals cause significant AoE damage as well as melee damage.  Once the elementals spawn, the arm that was destroyed will respawn in 60 seconds.

Strategy

Once engaged, Kologarn does not move at all during the fight, he stays in position in the area where the shattered staircase once was.  He must be tanked where he is. The fight requires at least 2 tanks and preferably 3. 

Two tanks must remain in front of Kologarn and in melee range at all times so that he does not cast Petrifying Breath.  The second tank stays in position and remains ready to taunt off of the main tank if the crunch armor effect ever stacks to 2 stacks.  As soon as it clears, the main tank can either pull threat back or wait until the off tank has two stacks.  A well geared tank that focuses on avoidance can generally tank the whole fight, as any Overhead Smash that is dodged or parried will not apply the effect. 

[protip]As a tank it is relatively easy to avoid getting two stacks by saving avoidance trinkets and abilities for when you have a single stack of crunch armor applied to you already. Once you have one on you start using anything that increases the percentage chance that the boss will miss you or that you will dodge or parry the attack.  With any increased chance to dodge or parry it is extremely unlikely that you will be hit again.[/protip]

The third tank remains ready to grab agro on the elemental packs that spawn when an arm is destroyed.  For this reason a Death Knight or Paladin tank is best suited for this job with their AoE threat generation abilities.

Ranged players need to setup so that they can avoid hitting other players when they are chosen as a target for the Focused Eyebeams.  A common strategy is to have all ranged players spread out along the back edge of the room.  Then, when targeted, they take a few steps forward and run the longest way across the room.  Since they will be more than 5 yards from all the other players in the back row, and behind the players in the front doing melee, no one else will get hit by the eye beams.  Once the beam stops, they find a spot in the back row again.

Melee DPS moves in tight to the body with the tank and shifts between targets as required. It is important to note that even though the arm’s graphic appears to be beside and in front of the main body, melee DPS should stay facing forward at all times.  If they turn to face the arm, it will in fact move in and out of range.  If you face forward you can always hit the arm.

Since the right arm causes the most issues in the fight by gripping players and keeping them held until dead or forced to let them go, it will be the focus for all damage. Once the fight starts, everyone focuses on the arm until it is destroyed.  Any time someone becomes gripped, a designated healer will keep them alive until freed. 

Whenever an arm is destroyed two things happen.  The first is that the arms starting health is deducted from Kologarn, meaning he loses roughly 15% of his health.  The second is that a pack of elementals spawn where the arm was that need to be picked up by the add tank.  The add tank then moves them away from everyone else and lets ranged DPS know when they can AoE them down.  Melee DPS focuses on Kologarn unless called for. Once the elementals are down, everyone works on Kologarn until the right arm respawns again.

Once the group has destroyed an arm, the elementals, worked on the body and seen the arm respawn, they have seen the whole encounter.  The fight then simply continues with the group following the same process over and over until Kologarn is defeated. 

[protip]If both arms are down at the same time Kologarn gains additional abilities.  Therefore you should pay attention to the health of the left arm and switch to it if needed.  It is best to remind players to not damage the left arm if possible though, so that you can remain focused on the right.  Multiple target effects, AoE and other damage can spill over to it however, so it is best to keep an eye on it.[/protip]