You must have completed the key quest within VT from the quest npc's to receive the key to accessing the boss. If you have the key and have killed Jaxxyurn Kor Luythri, outside the room is a black statue with hands holding an orb. You are able to click this to be teleported to the hallways that lead to Talriem.
The Fight
PHASE 1
There is a lot of trash in these halls. It is recommended to use a bard with fading memories and COTH to save time.
There are two npc's of Talriem up on opposite ends of the zone. They do an HP check every 5%, where the two have to be within 1% of each other or they heal 10% HP.
Have two groups set up at each one and do equal DPS until they die.
PHASE 2
Talriem respawns in a larger square room equidistant from the two locations of phase 1. There is a lot of trash on the way back through the halls. Either have a bard use fading memories + coth to the new location, or kill your way through quickly.
This is a tank & spank. DPS as hard as you can. He will summon very many adds and become immune after an X amount of time repeatedly through the fight. If your DPS is high you will not experience many of these. The adds don't do anything special, they must be killed to kill Talriem. When they die, he is no longer immune and can be continued to be dps'd.
Loot
