You see a thorn steed
Notes
It's the mount of the Thorn Knight and it looks like a Flamesteed. It's part of the Forgotten Knowledge Quest.
Abilities
Unknown.
Damage Taken From Elements
Physical 
Death 
Holy 
Ice 
Fire
Energy
Earth
Location
A dungeon here, accessible through the Desecrated Glade.
Strategy
Do not use Death Damage against it otherwise it will heal 10 times the damage it was supposed to receive.