You see a sword of vengeance.
Notes
It is an animated Justice Seeker (albeit facing the other direction). Swords of vengeance spawn next to The Last Lore Keeper. Part of the Forgotten Knowledge Quest.
Abilities
Damage Taken From Elements
Physical 
Death
Holy
Ice
Fire
Energy
Earth
Drown
Location
Final boss room of the Forgotten Knowledge Quest.
Behaviour
Unknown
Strategy
Unknown