Caella of the Pearl must be kept in the center circle where she stands. If she gets pulled out, then she gets additional buffs which can cause raid wipes. She has 2 AE's which are both ranged based on damage. The further away you are, the less damage you take.
Pearlescent Shock - Cureable Elemental - If not cured, players gets stifled and put in time-out for 60 seconds.
Touch of Absencia - Incureable Truama - temporary stun attached to this.
Along with the 2 AE's, Caella does an emote where she says, "I cleanse myself of your impairments!". When she does this she wipes all debuffs and spikes damage for about 3 to 5 seconds. The main tank will need to use skins/blocks to survive while debuffs and heals catch up.
There will be a total of 9 common adds named a coerced combine guardian. These can be controlled by a good AE off tank. Have your raid use singular focus and stay away from blue AE's to keep from damaging the adds. As soon as one of these 9 dies, it will repop shortly. The small adds put a curse debuff on players on occasion that give -500 hate gain to tanks and +500 hate gain to non-tanks. Cure what you can, but prioritize keeping the tanks cured. These curses can also be cleared by running under one of the waterfalls around the room if necessary.
The 9 adds cast a single target cureable trauma debuff that lowers the mitigation of the player. This will cause some serious spike damage on your tanks, so make sure you cure it a.s.a.p.
Along with the 9 adds, there is a siren controller that spawns roughly every 45 seconds or so. This siren can spawn in 1 of the 6 pools around the room and must be pulled into the raid and burned. If the siren is not killed within roughly 20 seconds, then it will target a healer in blue text and all of the adds and named will focus kill that healer. If the first siren is not dead by the time the 2nd siren spawns, then they cast a raid wide healer debuff that is pretty much a wipe.
We had our raid setup on the left side closer to the 3 pools so that we were guaranteed to kill any of the ones that spawned on that side before the blue text healer death. The ones from the other side always managed to kill 1 healer, but we were able to recover from that death with quick res'ing and temps. If your raid has enough dps, you can setup in the center and try killing the sirens from either side before they call a death target.