Before Pull
Pop a Nature protection potion.
Phase one
Casters/healers will be on the platform while melees are doing the “dance”.
Not much to heal here neither, so you have more than enough mana to cure disease on melee (which lower their HP pool).
Keep an eye of hunter’s pet, as they won’t do the “dance” correctly.
Keep away from the boss, it does a mana burn AOE.
Phase two
You’ll have to “dance”, like melees were doing during P1. If you’ve never done, just follow the others and don’t try to cast heals off (don’t take risk, survive, just throw renews and shields).
If you know the fight better you’ll have time to throw flash heals between two green explosions.
You can self shield throughout the dance to avoid bad surprises
Teleport
During P1, you can get teleported in the other room. Wait for other people to get teleported with you and follow them to reach Heigan room.
You’ll have mobs attacking you during the run. Try to heal the people with you without taking agro. The best way to do that is to spam fade on cooldown and use shields (does not create agro) rather than heals (you’ll have to heal at some point obviously, but prioritize shields).