Giant Bavorois still kills me occasionally!!! >:-(

[SniperRifle]

Liquid Aura.

[CalvatE]

Liquid Aura.

That boss, from time to time, aggro other members of the party and the tank can't do anything about it, no one can, and after a short while, the boss will return to the tank if he/she is the one with most hate.

Few things you can do besides keep running, maybe using spring to get away faster, is casting Stoneskin and/or the water spell to push the boss (don't know if that will work but you can try it).

He's a level 50 Arcanist, not a Conjurer.

Though Maraf is right, throughout the fight the boss will target someone, "Focuses target on--" and a crosshair goes over that player where it then seeks them out and wont stop until it does its flail.
The trick is to just plain keep away. It'll throw a fireball at you, and then shortly after flail. Just keep away the best you can.

Its flail goes off regardless how close it is to the target so if you're not being targeted then go hide in the corner, it usually wont walk there because people circle the room.

After it does its flail the tank should get aggro back right away. But during the time in which it targets someone, it wont ever lose focus so the Tank can't get it back until the end.