I am putting SS on the tank, but everyone with voodoo (including tank) is still taking damage...wtf. I feel like it worked on normal, but when my guild tried heroic the other day my spirit shell did nothing. Power word: Shield works great though. Anyone know what's up?
Shadowy Attacks (that's the name of the ability) by the boss bypass absorption mechanics. The shadow bolts and grasps by the adds should not. That being said I think they may have made an adjustment on this fight so that it is not so substantially easier for disc healers as opposed to other healers by making absorbed damage still hurt the voodoo dolls.
Just a clarification on how absorbs work on this encounter.
Any attack with the exception of Shadowy attacks absorbed by someone that has a voodoo doll will carry over when that damage is copied over to the other Voodoo dolls. If I take 100k damage and 10k if it is absorbed, I only take 90k damage and the other Voodoo dolls also take 90k damage.
For Shadowy Attacks, they don't actually bypass absorption in the way that you might think because when the tank receives one of the four types of Shadowy Attacks absorption effects are infact absorbing that damage (This is shown on World of Logs if you want to see for yourself). What actually happens is that the Shadowy Attack damage will always copy the full amount of damage over to the Voodoo Dolls regardless of how much of it was absorbed. So in a way it does bypass absorption, but the dungeon journal is rather misleading in how it does so. It implies that the damage itself bypasses absorption when in fact what it really means is that it ignores absorption when calculating the damage to copy over to the other Voodoos. This changes the rules a bit, so let's take the same situation above and apply that to Shadowy Attacks:
Tank takes 100k damage from a Shadowy Attack and 10k of it is absorbed. All other Voodoo Dolls still take 100k damage despite that partial absorption.
Tank takes 100k damage from a Shadowy Attack and 10k of it is absorbed. Another Voodoo Doll will take 100k damage, but this time that secondary Voodoo Doll has their own 10k shield. They take 90k damage.
In any case this doesn't actually change how to beat the encounter (A good rotation of defensive cooldowns). It's just that Spirit Shell is still effective against Shadowy Attacks on its primary target, but won't reduce the copied damage like it would had it been any other attack.
It's worth mentioning if you're stacking Spirit shell on tanks that the maximum absorb value caps at 60% of the casting priest's health. In most fights tanks are getting hit too frequently for it to matter much, but useful to consider nonetheless.
Tank takes 100k damage from a Shadowy Attack and 10k of it is absorbed. All other Voodoo Dolls still take 100k damage despite that partial absorption. Tank takes 100k damage from a Shadowy Attack and 10k of it is absorbed. Another Voodoo Doll will take 100k damage, but this time that secondary Voodoo Doll has their own 10k shield. They take 90k damage.
I'm skeptical about your explanation about Shadowy Attacks' damage can be "reduced" by absorption since that's not the way I saw it worked (well, I'm a dps, so I could be wrong since I didn't really pay much attention about it). However, I know the bolded part is wrong, unless they changed how it works recently. Voodoo Doll' damage are always copied 100% on other Voodoo Doll targets, regardless of whether they have their own cd, a shield, or w/e on them.
During my attempts on Garajal H 4 (or 5?) weeks ago, there was a time I got Dolled, dropped down to ~20% hp, my Divine Aegis proc'd, I immediately use Fade (so there is no adds' damage on me) & Dispersion just to get killed right after that. Logs / Recount Death showed that I still got hit by ~200k damage, through the 90% damage reduction of Dispersion (and probably through Aegis, too, seeing I take no adds' damage to break the shield).
As others have stated, Spirit Shell / PW:S are good on this fight since they are double-dipped on dolled targets, not because they can directly lower Vodoo Doll damage. They can't reduce S.A damage, but they absorb melee hit / adds' damage well (in turn lower other Dolls' damage) and that's the majority of incoming damage in the fight.