- Be sure to clear the malformed geodes - even though they're not aggro, they'll get in the way during one of the boss fights.
Unatu starts the fight by putting you under an incurable detrimental that causes him to do more damage to you the closer you are to him. In solo difficulty, this doesn't seem to matter much. He will put a curable trauma detrimental on you. If it isn't cured in time, Unatu will emote in red that he is "preparing to shatter you." If his ability isn't interrupted, he hits you with Stoneshatter, which does about 160K and transfers full agro to you.
You will want water breathing for this one because Poxrata will cast a spell that fills the room with water. I focused on Brudu, Grudu and Krudu first. Once they are defeated Poxrata will be at low health. Finish him off for the win.
During the fight, the Earthen Behemoth will repeatedly emote that your attacks have knocked off parts of it. After the emote, 4-5 dislodged stones will join the fight. They're extremely weak and go down easily. The Earthen Behemoth also has a multi-target trauma detrimental to cure.
The Vathsis will periodically emote that it is drawing upon the portal's power, then summon an infused effigy. The infused effigy in turn "coats The Vathsis in a mana-draining venom" - it must be burned down before The Vathsis can be attacked without triggering a power drain.
At about 95% health, Kavis Set'Ra will run away.
There is a pillar in the middle of the room, and three ledges on the walls to the South, West, and East. A Shade of Kavis will appear on each ledge. To get to those ledges, you must run up to the pillar from that direction and you'll be teleported onto the ledge. You'll also get a curable arcane detrimental. In order to damage the Shades, you must engage a Heroic Opportunity. Once the Heroic Opportunity is completed, the Shade will turn into a Reflection of Kavis which can simply be killed. Once you kill it, drop down to the floor.
Down on the floor of the room, there are four hooked brineterrors. Ignore them if possible - they don't run fast and if you kill one another one immediately spawns. Use the teleporter to get up on the ledges and eliminate all 3 Shades of Kavis.
Once this is done, Kavis Set'Ra will respawn with 29% health. He puts two different uncurable detrimentals on you - one is a poison DoT, and the other is a noxious resistance debuff. The noxious resist debuff stacks with itself and instances of the debuff are added the longer the fight goes. This is essentially a DPS check, you have to kill Kavis before the damage from the DoT becomes unmanageable.