Kel'Thuzad's Defeat (10 player)

Kel'Thuzad's Defeat (10 player) is a dungeon & raids achievement earned for defeating Kel'thuzad in Naxxramas on 10-player mode.

Strategy
This is not a timed fight, some frost resistance gear can be used to help mitigate the bosses aoe frost damage, even though it may hamper dps and healing. However, it is more common that the main tank will wear some frost gear, and the rest of the raid will not wear any, although a Frost Aura or Frost Resistance Totem may be used to assist healing.

Phase 1
During the first phase, all players must stay in the middle part of the room (inside the ring on the floor) while the abominations, banshees, and skeletons slowly engage. If any players or pets leave the ring, many additional undead engage at once.

Phase 2
Once the second phase starts, the boss should be engaged by the main tank, and any remaining banshees and other undead should be killed. Players should spread out to mitigate Frost Blast (an ice block effect only removed by healing) and Detonate Mana (aoe explosive debuff).

The ice block is an aoe - so any players closer than 10 yards will also be blocked, and all must receive a heal before being killed by the block. Because of this, if there are only 2 melee dps plus the main tank, they can spread out in a triangle shape, all at max melee range from the boss. However if there are additional melee, they should stack into 2 groups, and healers need to watch for multiple ice blocks.

It's very important that healers are in range of members of the raid so they can remove the ice block debuff. Healer positioning should be coordinated before the fight starts. It is recommended to position healers evenly around the room, rather than all in the center. This reduces your chances of losing 2 healers at once.

Also raiders should be on the lookout for Shadow Fissures that spawn beneath your feet. The player on the top of the threat list (hopefully your main tank) will not be ice blocked at any point during the fight.

Phase 3
During the final phase, everything is the same except additional Guardians of Icecrown are released and must be picked up by one or two off tanks. These will never be killed, they just need to be kept busy. Off tanks must be cautious when picking up the adds to maintain a distance from other other raiders, especially healers. An ice block on a tank and a healer, on top of guardians running around free will almost certainly cause a wipe. If possible, off tanks should be within taunting range of each other, so if one tank dies, recovery is possible. Off tanks should also carefully position the adds and their camera so they can still watch out for fissure spawns.

Once Kel'Thuzud has been defeated, the fight immediately ends and the guardians will run away.