You see a death dragon.
Notes
Apppears in the Ferumbras' Ascension Quest with Ragiaz.
Abilities
Unknown.
Damage Taken From Elements
Physical 
Death 
Holy 
Ice 
Fire
Energy
Earth
Drown
Location
Ferumbras' Ascension Quest quest area.
Behaviour
Unknown
Strategy
Every time you kill one, another appear, try to trap them in north.