ICC - Lady Deathwhisper

Lady Deathwhisper on Tankspot

This fight seems to be a lot like the Kel'Thuzad fight in Naxx
There seem to be 2 phases.

P1
Deathwhisper is in a mana shield. She will cast shadow bolts on random party members. It is needed that a few DPSers nuke Deathwhisper so her mana shield will drop. During the whole phase adds will spawn from both sides of the room. These adds need to be tanked and DPS-ed down.

Cult Adherents are immune to magic damage.
Cult Fanatics are immune to physical damage.

So proper damage types for different adds. Also she will cast an enrage on one of the adds from time to time. The prio is to get the enraged add down first.

She will also use Death and Decay on the raid. So dont stand in the green huge circles. Also shadow and frost resistance auras are useful here.

P2
When her mana shield drops she needs to be picked up immedietly by a tank since she never had an aggro table before. It is possible that she will stack a debuff on tanks that make them lose aggro on every stack but this is unconfirmed(so tank switching may be needed).

She will also cast frostbolt on main aggro target(tank) which needs to be interrupted so the tank doesnt get instagibbed.

She will also summon a vengeful spirit from time to time. The person it target needs to run away because they can't be killed. (like the beginning of some wing in naxx, possibly military).