Hello Blizzard,
Using the Throw Glaive ranged attack does not start the Gothik the Harvest fight. The “Immune” text is displayed when the glaive hits him, but the fight itself does not actually begin. I have to double-jump and use Fel Rush on him to begin with the fight.
Taunting works (my belf DH is dps spec but has taunt, I don’t know if it’s a talent I chose or came with being a DH in general though). I wish they’d fix the immunity not initiating the fight though, as I’ve ran into a few different classes that have issues starting the fight for this reason.
I believe Consume Magic also works.