This fight contains 4 Foreboding Statues around the room. Keeping them alive to block his tether is the main mechanic of the fight. His moves are as follows:
Geirothr: Inflicts magic damage to the tank.
Tether: A red icon will appear above a player's head and Anchag will raise his sword up to announce this move, before a tether attaches itself to the targeted party member (Can even target the tank). Whoever is targeted must run behind a Foreboding Statue to block it, or it will inflict damage and stacking debuffs of Vulnerability Up, and Febrile to whoever is hit. Getting hit once or twice is survivable (And the first time it is used in the fight will only hit 3 times), but taking all four hits will most certainly kill. The tank is especially vulnerable, as being in melee range will make it difficult to run behind a statue and the debuffs will make tanking more difficult.
Valfodr: A line AoE that stretches toward a random party member. This AoE line WILL move to match the player's movements, but can be mitigated somewhat by being in melee range. This move can damage the statues.
Hall of Sorrow: Targeted AoE on a random player. This can hurt the statues, so don't stand nearby them during the fight.