Before Pull
There will be 3 tanks and you need to assign each heal to a tank. Assign someone to hot warlock kife tap.
The fight
The 3 tanks are the only ones that need healing (as well as warlock life tap). The melee decrease their HP on purpose, do not heal them.
The two “hatefull strikes tanks” will get 6k hits that needs to be insta top. So basicly, you only focus on the tank you are assigned to and you spam R5 Greater Heal.
If the hatefull strike happens while you’re casting, you let your GH go out. If it does not, you’ll have to cancel your heal casting not to get oom too early.