Shirrak the Dead Watcher

Abilities

Carnivorous Bite: A DoT bleed attack

Focus: Shirrak will occasionally focus his attacks upon one player, he emotes "Shirrak the Dead Watcher focuses on (Name here)!" Also a flare will appear near the targeted player, make sure they move quickly to avoid the oncoming assault of 3 small AoE blasts each dealing 1500-1800 damage.

Inhibit Magic: Increases casting time by 50%, this can stack up to 4 times

Fight

Have your tank run up the stairs and aggro Shirrak, he should tank him in the center of Shirrak's room with DPS and healers spread out in a circle around the boss. The inhibit magic will stack quite quickly to four and increase spell casting duration by 200%, making all those heals and other spells that much harder to get off in time.

Despite the casting speed debuff Shirrak is quite easy if your party stays alert for the focused attack and moves out of range. Beyond that it's a simple encounter.

Exarch Maladaar

Abilities

Soul Cleave: All damage and healing is lowered by 50%

Dark Side: Creates a hostile shadow copy of the target player

Soul Scream: AoE Shout

Avatar of the Martyr: Summoned at 15% HP this avatar hits quite hard and has Mortal Strike as well

Fight

This boss is much more of a focus on targetting and strategy rather than a massive DPS overdose like some others. Basically your chance of success will be much higher, nearly guaranteed, if your party understands the need to kill the summoned dark sides whenever they appear.

Beyond his dark side summoning the Exarch does piddly damage really, the only surprise of the fight is the Avatar and even that dosen't pose much of a threat to the organized group. I'd recommend taking out the Exarch before killing the Avatar, makes the fight a bit easier