Baron Rivendare

Slaughter Square
Finish the abominations in the square to bring Ramstein out of the slaughterhouse. Ramstein's death is followed by an incoming wave and the Black Guard Sentries, so keep the group together instead of rushing the final door. Defeat the sentries before entering Rivendare's room, then establish the tank and ranged positions before the final pull.
Baron Rivendare
Elite UndeadRivendare combines a healing-reduction strike with persistent nearby Shadow damage and summons that heal the boss if left alive.
Abilities

Unholy Aura
Causes the caster to automatically inflict 150 Shadow damage every 2 sec. to nearby enemies. The aura lasts until cancelled.
Keep ranged attackers and the healer outside Unholy Aura when their range permits; reserve continuing healing for players who must stay near Rivendare.

Mortal Strike
Inflicts 300% weapon damage and leaves the target wounded, reducing the effectiveness of any healing by 50% for 5 seconds.
Mortal Strike reduces incoming healing as well as dealing a heavy hit. Prepare tank health and mitigation before the debuff instead of relying entirely on a large heal afterward.

Cleave
Cleave also strikes allies near its victim. Keep the tank's side of Rivendare clear of the healer and other melee attackers.

Shadow Bolt
Hurls a bolt of dark magic at an enemy, inflicting Shadow damage.
Interrupt Shadow Bolt to free healing for the Mortal Strike victim and the players inside Unholy Aura.

Raise Dead
Attempts to raise an undead servant back to life to aid the caster in battle. After 12 seconds., if the servant still lives, it will sacrifice itself to heal the caster.
Destroy the raised servants before they sacrifice themselves to heal Rivendare. Keep an area-damage player able to protect the healer when they arrive.
Tank- Anchor Rivendare near a wall with your side of the boss clear for Cleave. Preserve mitigation and a health buffer for Mortal Strike so the healer is not trying to recover the entire hit through reduced healing.
Healer- Use the room's width to stand outside Unholy Aura while keeping the tank in range. Prepare the tank for Mortal Strike and bring pursuing raised servants toward the assigned area-damage player.
Damage- Move opposite the tank for Cleave, interrupt Shadow Bolt, and immediately destroy raised servants before they heal Rivendare. Ranged attackers should not stand inside Unholy Aura merely to stay near the boss.