You see Shadow of Marziel
Notes
This boss is only found when summoned by Arthei. Therefore, it is not possible to confirm the amount of its health points nor its loot.
Abilities
Unknown.
Damage Taken From Elements
Physical 
Death 
Holy 
Ice 
Fire
Energy
Earth
Location
Vengoth Castle (when summoned).
Behaviour
Unknown.
Strategy
Treat him as Marziel.