This is a nice post from BossKillers. Re-posting it here for easy access/read.

This encounter is a two phase fight, during which your raid must not only kill Lady Deathwhisper, but also her plentiful and devoted followers. During the first phase of the fight, Lady Deathwhisper will shield herself from harm, and her followers will attack your raid in waves. Not even death will stop them from protecting their mistress, so be wary of the corpses around you: Lady Deathwhisper will revive them to fight again. Once your DPS has exhausted Lady Deathwhisper’s shield, she will cease calling followers, and instead start to melee attack. During this second phase, the main challenge will be to interrupt her attempts to cast a massive Frostbolt at your tank, while your DPS continues to bring her down. You’ll have 8 minutes to complete both phases and kill her, before she gets really angry.
Raid Preparation
An appropriately geared raid for this instance will have spent some time gathering equipment in Trial of the Crusader. You will want most of your raid members to have a majority of item level 245+ gear for the 25 man version, and 232+ for the 10 man version. In the same way that Lord Marrowgar is a “gear check” for your tanks and healers, Lady Deathwhisper is a “gear check” for your DPS. She has a ten minute hard enrage, and in this time your DPS must put out enough damage to burn through her significant mana shield, the life pools of 20+ adds, and her own life pool as well.
As always, your raiders should be prepared to utilize the usual assortment of consumables: flasks/elixirs, buff food, and potions, should all be used in order to have the best chance at success.
Raid Composition
25 Man
2 tanks – Both will need to pick up and control multiple adds in Phase 1, and both will need to take turns serving as the Main Tank (“MT”) for Lady Deathwhisper herself during Phase 2.
5-6 healers – You will want to assign 1-2 healers for each tank, and have another 2-3 healers assigned to keeping the raid healed up from the various randomly targeted damage effects.
17-18 DPS – It is very important that your raid have an even balance of physical and magical DPS, because there are adds which are immune to each type of damage.
Having a shaman for Heroism/Bloodlust is nearly mandatory because of the enrage timer. You will want several players with quick and reliable Crowd Control (“CC”), to neutralize the members of your raid who become mind controlled. It is also quite helpful to have at least one player who can decurse and another who can remove diseases. Having either Misdirect from a hunter or Tricks of the Trade from a rogue (or both) can be helpful to make sure that Lady Deathwhisper gets picked up smoothly by your tank when she transitions between phases.
10 Man
2 tanks – Both will need to pick up and control multiple adds in Phase 1, and both will need to take turns serving as MT for Lady Deathwhisper herself during Phase 2.
2 healers – You will need two healers that can cover the tanks and also the raid between them; it will be very difficult to put out the damage needed to keep up with the add spawns and still beat her enrage if you have 3 healers.
6 DPS – It is very important that your raid have an even balance of physical and ranged DPS, because there are adds which are immune to each type of damage.
Having a shaman for Heroism/Bloodlust is nearly mandatory because of the enrage timer. It is also quite helpful to have at least one player who can decurse and another who can remove diseases. Having either Misdirect from a hunter or Tricks of the Trade from a rogue (or both) can be helpful to make sure that Lady Deathwhisper gets picked up smoothly by your tank when she transitions between phases.
Mobs and Abilities

Lady Deathwhisper
She has 13.9 million mana and 13.4 million health in 25 man.
Mana Barrier – This is a bubble around Lady Deathwhisper, which will instantly heal any damage done to her for as long as she has mana to maintain it. It consumes her mana at a 1:1 ratio for each point of damage that would have otherwise been done to her health.
Details
Shadow Bolt (Phase 1) – This is a 2 second cast ability that is used on random players throughout Phase 1. It is a single hit of ~7-9k shadow damage that just needs to be healed up.
10 man: Details 25 man: Details
Frostbolt (Phase 2) – This is a 2 second cast that must be interrupted. It is targeted on the acting MT throughout Phase 2. If she finishes the cast, the targeted person will take a 50k+ hit of unresistable frost damage. If the hit doesn’t kill them, their movement speed will be slowed by 50% for 4 seconds.
10 man: Details 25 man: Details
Frostbolt Volley (Phase 2) – This is an instant cast ability that Lady Deatwhisper uses throughout Phase 2. It has an 8 second cool down time, but she doesn’t always use it immediately. It will hit all players in the room (it has a 200 yard radius, centered on the boss) for 10-13k frost damage, and slow the movement speed of everyone it hits by 50% for 4 seconds.
10man: Details 25man: Details
Death and Decay – This is basically identical to the death knight ability, except hers is bright green instead of red and hits a good bit harder. It is cast in random locations throughout the fight. Don’t stand in it.
10 man: Details 25 man: Details
Dominate Mind – This is a 20 second mind control, periodically placed on a random player in the 25 man version of the encounter. While a player is mind controlled, their damage will be increased by 200%, and healing increased by 500%.
Details
Dark Empowerment – This is a buff that Lady Deathwhisper will periodically place on one of her adds. It affects each type’s behaviour differently, but makes all of them immune to interruption.
Details
Touch of Insignificance (Phase 2) – This is a stacking debuff that Lady Deathwhisper periodically places on her current target (the acting MT) that reduces the target’s threat generation with her by 20%. It stacks up to 5 times.
Details
Enrage – Lady Deathwhisper will enrage 10 minutes after combat with her begins, doing ~500% extra damage with all her attacks.
Summon Reanimated Adherent (Phase 1) – Lady Deathwhisper will revive one of the Cult Adherents’ bodies, as a Reanimated Adherent.
Summon Reanimated Fanatic (Phase 1) – Lady Deathwhisper will revive one of the Cult Fanatic’s bodies, as a Reanimated Fanatic.
Summon Spirit (Phase 2) – Lady Deathwhisper will summon a Vengeful Shade, which will rise from any dead body in the room, including those of dead players, and chase a random raid member.
Vengeful Shade – This summoned mob has a melee swing of around 200-300.
Vengeful Blast – if a Vengeful Shade gets within melee range of a player, it will explode for ~17-18k shadow damage, hitting everyone within 15 yards.
10 man: Details 25 man: Details

Cult Adherent
Frost Fever – This is a disease cast on random players, which lasts for 15 seconds, doing frost damage and slowing the movement and casting speed of the afflicted player. Keep this cleansed off anyone it hits.
10 man: Details 25 man: Details
Curse of Torpor – This curse is randomly cast on players as well, increasing the cooldowns on all of the player’s abilities by 15 seconds while it lasts. Keep this cleansed off anyone it hits.
Details
Deathchill Bolt – This is the Adherent’s main attack, hitting their current target for 6-8k specialized shadowfrost damage (meaning neither shadow resistance nor frost resistance has any effect on the amount of damage taken).
10 man: Details 25 man: Details
Shroud of the Occult – This ability is only used if the Adherent receives Dark Empowerment from Lady Deathwhisper. When used, it shields the mob from, and reflects onto the caster, all magical damage. It also absorbs 50,000 damage before breaking.
Details
Deathchill Blast – This ability is only used if the Adherent receives Dark Empowerment from Lady Deathwhisper, after the Adherent has used Shroud of the Occult. It will be targeted on a random raid member, and hit that person and all other raid members within 10 yards of them for ~9-10k shadowfrost damage.
man: Details 25 man: Details
Dark Martyrdom – This is a 4 second cast ability, which is immune to interruption. When the cast finishes, the Adherent will explode and damage any players within 15 yards.
10 man: Details 25 man: Details
Reanimated Adherent
The revived add will have all of the abilities it had before as a Cult Adherent, and will also have a buff called Adherent’s Determination.
Adherent’s Determination – This buff is always present on any Reanimated Adherents, and it makes them 99% immune to magical damage.
Details
Cult Fanatic/Reanimated Fanatic
Shadow Cleave – This is a basic melee cleave attack. It will hit any players in front of the mob in melee range for ~15-17k shadow damage.
man: Details 25 man: Details
Necrotic Strike – This is the Fanatic’s main attack, hitting their current target for 70% of weapon damage and leaving a debuff that negates the next 15,000 healing received by that player. It must constantly be healed through.
10 man: Details 25 man: Details
Vampiric Might – This self-buff will only be used if the Fanatic receives Dark Empowerment from Lady Deathwhisper. It increases the mob’s damage by 25% and heals the mob for 300% of it’s damage dealt. It lasts 15 seconds, so the mob should be CC’d until it falls off.
Details
Dark Martyrdom – This is a 4 second cast ability. When the cast finishes, the Adherent will explode and damage any players within 15 yards. (Possibly interrupting this cast will prevent the add from being reanimated)
10 man: Details 25 man: Details
Reanimated Fanatic
The revived add will have all of the abilities it had before as a Cult Fanatic, and will also have a buff called Fanatic’s Determination.
Fanatic’s Determination – This buff is always present on any Reanimated Fanatics, and it makes them 99% immune to physical damage.
Details
Strategy
Phase 1
When your raid first engages Lady Deathwhisper, she will simply stand in place and yell a bit.
DPS can go full-force immediately, because she doesn’t follow any threat table for her attacks. Throughout the whole of Phase 1, Lady Deathwhisper will cast Shadow Bolts at random raid members, place Death and Decay areas randomly throughout the room, and heal herself with her Mana Barrier. In the 25 man version, she will also periodically mind control a random raid member who should be promptly crowd controlled. Phase 1 will continue until enough damage has been done to Lady Deathwhisper to completely exhaust mana pool through her using it to keep her shield up. Because her mana pool is roughly the same size as her health, Phase 1 will actually last longer than Phase 2. This is because your DPS will also have to deal with killing multiple adds during Phase 1.
The first set of adds will come ~15 seconds into the fight, and another set will come out every ~40 seconds after that until the phase ends. Cult Adherents and Cult Fanatics spawn from the alcoves along the side walls (see diagram A). In the 10 man version, one side or the other will spawn adds (1 from each alcove on that side). In the 25 man, both sides spawn each time, so there will be 6 adds coming from the alcoves. Additionally, a single add will come from the stairs where the raid entered Lady Deathwhisper’s room, bringing the wave totals to 4 for 10 man, and 7 for 25 man. In 10 man you can split the adds among the two tanks however seems convenient. In 25 man, each tank will need to take a side and pick up all 3 adds that spawn on their side, and one of them will need to watch for the lone 7th add and pick it up as well. The adds are CC-able, so use Shackle, stuns, etc. freely to control adds that aren’t being burnt down if it helps your raid to focus their damage more effectively. Shackle can be especially useful on the Cult Fanatics, as they only have melee-range attacks.
At this point, and continuing on until the end of the phase, DPS will need to move between killing the sets of adds, and doing damage to Lady Deathwhisper.
While there are adds alive, Lady Deathwhisper will occasionally pick a random add to cast Dark Empowerment on. Regardless of which type is chosen, it should be dealt with as quickly as possible, as it will become much more dangerous than any other adds alive. This is how to deal with them:
- A Cult Adherent who receives Dark Empowerment will use their Shroud of Occult and then start using Deathchill Blast. All raid members should quickly run away from the person targeted by the empowered add for the Deathchill Blast, while the Shroud of the Occult is burnt through by all DPS who deal physical damage, and then the add killed as quickly as possible by all DPS.
- A Cult Fanatic who receives the Dark Empowerment will at some point use Vampiric Might, quickly healing to full while hitting very hard. When it uses Vampiric Might, CC it until the buff wears off (15 seconds), then continue to burn it down. When the add doesn’t have Vampiric Might up, all DPS should kill this add as fast as possible. Your tanks should Taunt it off each other in order to kite it while it is killed, being careful to face the mob away from players in range of its Shadow Cleave.
If you are doing the 25 man version of the encounter, your raid must also deal with randomly mind controlled players once Lady Deathwhisper is engaged. These players should just be CC’d for the 20 seconds it takes the Dominate Mind to wear off.
Phase 2
Once Lady Deathwhisper runs out of mana and can’t keep up her shield anymore, she will begin to attack normally. It is critical that you have a tank free of adds to Taunt her at this time, and that all DPS stop hitting her until the tank has her firmly under control.
It isn’t important where she is tanked, just that she gets picked up before she can kill your DPS or healers. No more Cult Fanatics or Cult Adherents will spawn once Phase 2 begins, but if there are any currently alive they will still need to be killed off. Lady Deathwhisper will no longer reanimate their bodies once Phase 2 begins. As soon as all the adds are dead and all of your DPS players are focused on Lady Deathwhisper, use Bloodlust/Heroism and cooldowns to try to kill her as fast as possible.
Throughout Phase 2, Lady Deathwhisper will continue to cast Death and Decay, so players will need to continue to move out of it. She will also continue to mind control players if you are in the 25 man version of the fight, so they will still need to be CC’d. However, she will stop casting Shadow Bolts, and instead begin using her Frost Bolt ability on the acting MT. This Frost Bolt cast should be interrupted every time she tries to use it, or it may kill your tank. So, once Phase 2 starts, make sure that there are always good interrupters on the boss to prevent this from being successfully cast. She will also begin to use Touch of Insignificance on the acting MT; when this debuff has stacked to 2 or 3, your second tank should Taunt her, so that DPS aren’t forced to hold back out of fear of pulling agro. The tanks will need to continue to swap back and forth like this for the remainder of the encounter.
Lady Deathwhisper will also begin to periodically raise ghosts from random dead bodies in the room; these ghosts will simply target a random player and move slowly toward that person for about 10 seconds and then fade away. If they get within melee range of a player before fading away, they will explode for a significant amount of damage. So, everyone should watch for these ghosts and move out of their paths.
Ten minutes after she is first engaged, Lady Deathwhisper will enter a hard enrage. At this point, she will start killing players off in single hits, and you will have very little time to finish her off before everyone is dead. If your raid is consistently controlling and killing the adds, but not doing so fast enough to leave adequate time to complete Phase 2, you may need to simply spend a bit more time gearing up your DPS in the lower tiers of raid content so that they can kill everything a little bit faster.
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