Keep casting the seeker droid and you will eventually get a cast off. When you are deploying the seeker droid, he will try to interrupt you and apply lethal effects to the water. This will deploy a Seeker droid on top of it. One of the group members need to go to the crystal rock he broke and click it. Make sure you stand on a platform when this happens and not in the water. At 75, 50, and 25%, he will stun everyone and jump to the ritual altar.When this happens, he will break one of the crystals behind him and becomes immune to damage. Lord Tagriss has some interesting mechanics you need to be aware of.

When the stun wears off, make sure to interrupt his Dread Tentacles, which will heal him otherwise. The canister will explode, stunning the boss and remove the effect of Dread Carapace for a short duration. This will cause the miniboss to land on top of the canister. After you kill the last tentacle, run to a Arcanum Bio-Containment Canister on the ground and stand near it (make sure to attack the Dreadseed Corruption growth on top of them to expose the canister). The miniboss will soon disappear and spawn four tentacles. This is a 3.5s cast that allows the boss to gain 1 stack of Dread Carapace, which reduces the damage it takes.

It will periodically cast Ichor Spit followed by Triple Tongue Frenzy. It has an interesting mechanic to the fight. Up ahead is the Corrupted Sithspawn Experiment. In one of the rooms you will find a second datalog. If you see a force field turn yellow or red, it is able to break releasing mobs into the hallway. Supply the power cell to the field turret will gradually charge up the turret which can one shot all mobs and finish the encounter (takes a lot of power cells to get it active) Supply the power cell/battery to the force field will make it stronger and prevent mobs from escaping into the hallway. There are power cells at each end of the hallway you can use to either power the turret or give power to the force fields. Up ahead you will find a hallway with a holdout type of scenario. The first datalog to start the bonus is located on this table not far from the entrance.

There is a bonus quest to get all four datalogs. The entrance is well hidden behind some ice rocks. Not the easiest entrance to find, follow the dotted line on the map.

Enter the Corrupted Jedi Temple on Ilum.

Seeker Droid (can be used as an ability).

Dreadseed Armor or Star Forager’s Jacket (Bind on Legacy).

You will make a decision at the end (light or dark) that grant you one of two chestpieces Dreadseed Armor (left) or Star Forager Jacket (right) for dark and light choices respectively. This heroic can be done with 3 players with a healer, tank and DPS.

Kotor wall panel puzzle