Find this one at the Twilight Highlands.    The instance starts off with a bombing run, not a fight, just enjoy the ride.

General Umbriss

• Bleeding Wound - 8000 physical damage every 2 seconds until healed to at least 90% hp
• Blitz - Charges random players, damaging and knocks back all players in the path
• Frenzy - Increases damage and attack speed by 50%, used at 30% hp
• Ground Siege - Inflicts 35K physical damage to all players and stuns them for 4 seconds

Notes:

• Heal bleeds
• Spread out to minimize Blitz, can sidestep it
• Heroic:  Shockwaves and Summons Malignant Trogg, explodes on death and makes Umbriss frenzy if killed near him, so DPS kite away and kill.

Forgemaster Throngus

• Impaling Slam - 8K damage every second for 5 seconds to random player
• Mighty Stomp - Creates Cave In doing physical damage to all who stand under it
• Pick Weapon - Changes weapons (and ability) every 30 seconds or so
• Mace - Gains Encumbered reducing movement speed by 70%, increasing physical damage by 300%, also randomly charge and impales player on his mace dealing damage over time
• Shield - Gains Personal Phalanx decreasing damage taken from the front by 99%, summons Twilight Archers to attack (cannot be targetted)
• Swords - Gains Dual Blades increasing chance to hit by 20% and giving each attack a chance to gain 2 extra attacks

Notes:

• If Mace, kite
• If Shield, DPS stay behind him, aoe heal
• If Swords, heal tank a lot

Heroic:

• Disorienting Roar - Reduces attack and casting speed by 50% per stack, each ability use depletes a stack, starts with 3 stacks.   
• Mace leaves trail of fire as he walks.   
• Swords puts magic DoT on tank, dispellable.   
• Shield turns into fire breathing dragon doing 8-10K fire damage

Drahga Shadowburner

Phase 1 (100-20%):

• Burning Shadowbolt - 9000 shadowflame damage to random target, interruptable
• Innvocation of Flame - Summons a Invoked Flaming Spirit that targets a random player and chases them, with a big red beam between the 2.   If caught, explodes for 50K
• Twilight Protection - Reduces damage taken by 90% while summoning Valiona

Phase 2 (Fighting Valiona):

• Valiona's Flame - 25K shadow damage frontal attack, knockdowns for 2 seconds
• Poison Clouds - To not stand in
• Shredding Swipe - Inflicts 100% damage and leaves a void zone on the ground
• Twilight Shift - Valiona leaves the fight abandoning Drahga, resume P1

Notes:

• Fight is basically Drahga to 20%, summons Valiona, kill her, she escapes in the end, resume fight with Drahga
• Kill fire spirits ASAP while kiting
• Stay way from purple fire void zones / green gas

Erudax

• Bind Shadows - Drains 5000 life every second and roots player within 8 yards of target
• Enfeebling Blow - Inflicts 75% weapon damage as shadow, knocking them back and cause their mind to become Feeble, increases damage taken by 100% for 3 seconds.
• Shadow Gale - Channels Gate of Shadow increasing shadow damage done over time to enemies not in the eye of the Shadow Gale
• Summon Faceless Corruptor - Who has Twilight Corruption channelling energies into corrupting an egg

Notes:

• Stand in the Shadow Gale (dark spiral on ground)
• Afterwards, kill Faceless Corruptor (can be snared) as it tried to run to and corrupt eggs. 
• If it succeeds, 2 Twilight Hatchlings spawn and flies up to randomly cast Twilight Blast (10K damage) on players
• Corrupter also casts Umbral Healing on Erudax healing him for 20% of his HP.
• Tanks could allow knockback of Enfeebling Blow to occur to allow time for Feeble to wear off.
• Heroic:  2 Faceless Corruptors spawn