Arzhan-Tin, The Ceaseless Fury, is a powerful Pyromancer and uses fire magic. He will spawn enemies and flee when you first encounter the deadly mage. Continue chasing Arzhan-Tin, and eventually, you will battle where you defeated Uryks Necklace-of-Ears. Any damage you inflict on Arzhan-Tin before this battle carries over to the fight.
Tips and Tricks for Arzhan-Tin, The Ceaseless Fury
Arzhan-Tin, The Ceaseless Fury has very telegraphed attacks. As long as you keep a reasonable distance and fight carefully, you shouldn't have too much trouble taking down this mage. One thing to note is that Arzhan-Tin's fire attacks will do residual fire damage to you if you are hit.
The most annoying attacks this Pyromancer has are its flame whip and spinning fire orbs. These can have deceptive timings at first, but both move fairly slowly, giving you ample time to roll out of the way.
If you get close to Arzhan-Tin, the mage will swipe at you twice with a sword, but you can roll behind him and avoid this. The last attack this mage has is summoning several firebombs. Simply avoid standing in those spots, and you will be fine.
Where to go after defeating Arzhan-Tin, The Ceaseless Fury
After defeating Arzhan-Tin, The Ceaseless Fury, you can either speak to the tree above the guardhouse or hunt down the second mage, Celus Zend, The Mourning Winter, in Ashbourne Village. If you speak to the tree, you gain the Runekey to go to Bol Gerahn through the Mirrorgate in Pardoner's Vale. If you want to hunt the second mage, travel to the east side of Ashbourne Village.
For more information on Salt and Sacrifice, check out How to become Guiltless in Salt and Sacrifice and How to beat Uryks Necklace-of-Ears in Salt and Sacrifice on Pro Game Guides.