Before Pull
Ideally, get 5k+ HP. But as priest it’s not mandatory, because you can levitate to avoid fall damage. Make sure you have light feather or noggenfogger to pop levitate /slowfall for fall damage.
The fight
There are 2 type of stuff to tank, at opposite side of room. So the tanks will move a lot, be far away from one to another, ect …. Keep an eye on their position, on their HP when they are out of range and stuff like that. Always start precasting when they pick up a new mob, that’s usually when healers are not focus on them and when there is a risk. Also keep an eye on the hunter that helps the tanks.
Some people will get throwed up in the air, damaging them for about 5k damage. The cause is a big ground fissure, the more people are stacked up, the more people will get rekt. So yeah, just top those guys up when it happens and try not stack with other healers (if 12 healers get this stuff at the same time, it’s kinda rip). If you’re affected by this ability, use levitate to avoid fall damage.
And the last thing is to keep an eye of the mages / warlock that will aoe some bugs. Precast / pre shield them. Don’t let them die!