Icecrown Citadel - Lich King

Lich King main abilities:

Infest (Raid Wide DoT about 25 seconds CD):
The lich king does about 10K, and a high DoT that gets removed when the target has more then 90% health.

Necrotic Plague (Very high DoT):
The lich king puts a massive DoT on a random player that will kill it in a few seconds. This needs to be dispelled. When it is dispelled, the plague will jump to the nearest target, that includes the lich king Adds, and you should pass it to them. Making it jump to another target will also increase the lich kings power. If fades after a few jumps but the more it jumps the more damage it does.

Remorseless winter (Massive AOE):
The lich king does about 10K damage/ second.

Pain and Suffering (AOE DoT):
About 3K damage/sec, can be stacked up to 5 times.

Defile (AOE):
High damage AOE that gets larger whenever a player gets inside it. Soul Reaper (Debuff): The lich king will place a Debuff on your tank that will cause a massive damage on it (about 55 K) after 5 seconds.

Harvest soul: (DoT, 70 seconds CD):
About 15 K damage (in 25 man) ever second. When it ends the target (if still alive) is transferred to Frostmourne.
Lich King tactics Step by Step:

This tactic plan requires 2 tanks

Lich king Tactics step 1:
If you have a disc priest shield as many players as possible (will help with infest later)
don't pull with MissDirect you will need it later. Therefor wait until tank gets good aggro before starting DPS

Lich king Tactics step 2:
Have the tank pull the lich king to the edge of the platform

Lich king Tactics step 3:
The Lich king opens with infest, quickly top off all the players for more then 90% so the DoT is removed. Do so every time Infest is cast.

Lich king Tactics step 4:
The lich king summons the adds.
Ghouls should be picked up by the tank, but do not DPS them directly.

Lich king Tactics step 5:
When Shambling horrors spawn you should misdirect to get them on the Off Tank and make sure they are tanked facing away from the raid. When they get enrages tranquilize them or stun them.

Lich king Tactics step 6:
When lich king casts Plague on a player, have the player stand next to an add (preferable ghoul) and then dispel it to make it jump to the add. Eventual it will reach a horror and will hopefully kill it as well.

Lich king Tactics step 7:
Before the lich king reaches 70% and changes phases kill all the adds, and dispel the plague off the adds Off Tank when he stands alone so that it doesn't jump to anyone else, and the buff is removed from the lich king. Also make sure you don't cross the 70% line when a new horror is about to spawn.

Lich king Tactics step 8:
At 70% the lich king moves the middle of the platform stats the transitional phase that will last 1 minute. He will cast remorseless winter and summon adds.
Because he was tanked at the edge it will take him several seconds to get to the middle of the platform. Quickly run to the edges of the platform to avoid this damage. (a new extension of the platform is formed in this phase)

Lich king Tactics step 9:
The lich king will also summon raging spirits to spawn from a random player. These melee hard and have a frontal cone shape silence, so have OT pick them up, face away from the raid, and kill them ASAP. 3 spirits will be summoned on the targeted player in total.

Lich king Tactics step 10:
Orbs will start floating towards raid member and should be killed, or else when they reach the target it will get a lot of damage, and will be thrown off the edges of the platform.

Lich king Tactics step 11:
While all of this goes on stay relatively spread to avoid as much of the damage of Pain and Suffering as possible.

Lich king Tactics step 12:
When the lich king ends this transitional phase quickly run back to inner platform because the platforms extension will collapse.

Lich king Tactics step 13:
Phase 2 starts.
Have the lich king tanked in the middle of the platform.

Lich king Tactics step 14:
The lich king will start casting Defile (dark cloud like AOE). Avoid getting in it is high priority because otherwise it will spread and cover the whole platform and you will wipe.

Lich king Tactics step 15:
When you run out of defile try to run to it's left and right edges (when facing the middle of the platform) so that if you're targeted by a Val'Kyr (read below) you will not be pulled above the defile, or too close to the edges of the platform.

Lich king Tactics step 16:
The lich king will summon Val'kyr Shadowguards that will attempt to pick up raiders and drop them off the edges of the platform. They need to be killed ASAP. They can also be (and should be) slowed.
This may get tricky when the Val'kyr moves threw a Defile AOE zone.

Lich king Tactics step 17:
After soul reaper is applied rotate your tank.

Lich king Tactics step 18:
Before reaching 40% kill a Val'kyr so it's not alive while transitioning.
When the lich king reaches 40% another transitional phase occurs. Repeat what you did in the first one. This time 4 spirits will spawn.

Lich king Tactics step 19:
Phase 3 starts and the lich king starts summoning vile spirits that will first over the lich king's head for a few seconds, and then attempt to explode on your raid. Because of this, spread out your raid, ans kill them before they reach the players to avoid as much of the damage as possible.

Lich king Tactics step 20:
Infest and Val'kyrs will stop at this phase.
The lich king will start casting harvest soul on random players. They need to be healed threw the DoT. Use damage shields and damage reduction to make sure they don't die cause it hits hard. When it ends they will be transferred to frostmourne
Players transferred into frostmourne will watch a battle between King Terenas and a spirit. They can either Heal King Terenas or DPS the Spirit. Either choice will result in the Spirit's death and the player will escape frostmourne. It is advisable to stun the spirit is possible when it starts channeling or interrupt it. If you die inside (you have to escape in 60 seconds) the lich king will gain a big buff for 15%.

Lich king Tactics step 21:
At 10% The lich king will kill the whole raid. Do not release and watch the ending scene. You will then be resurrected.