Kologarn: Right hand down
Strategy
As the gang proceeds up the stairs from the Antechamber, you will see a broken bridge called La Pasarela Shattered. Kologarn will appear to stand in the gap in the broken bridge (seemingly appearing out of nowhere) and will stare at the gang.
Everyone should go through the door and look towards Kologarn. This boss will remain immobile so ranged DPS won't have to worry about aggro. Melee DPS obviously can't be placed on his back because a piece of bridge is missing. To start the fight you just have to make the tank charge against him!