Blizzard is making an adjustment to the Lich King encounter in Heroic Icecrown Citadel, making it so damaging the Lich King, Raging Spirits, and Vile Spirits will be significantly reduced after Harvest Souls is cast. This change will be on the PTR for testing soon.
This change will cause all damage inflicted to the Lich King, Raging Spirits, and Vile Spirits to be dramatically reduced for the following 45 seconds after the Lich King has cast Harvest Souls to transport the raid into Frostmourne during Phase 3.A common tactic we are seeing to deal with this part of the phase is to have classes that have the ability to self-resurrect deliberately die before the Harvest Souls cast when the raid group is drawn into Frostmourne, and then accept a resurrection outside of the Frostmourne room to be able to continue to damage the Lich King while he is essentially inactive during this 45 second window. While our adjustment is definitely a change from how the fight behaved in 2009, we do feel that this would have been adjusted back in 2009 if it were more prevalent, as it encourages the stacking of certain classes to potentially trivialize part of the phase.We plan to have this adjustment deployed to the PTR via hotfix very soon.
Read more on wowhead.com