When you enter the arena, sprint or walk towards him while keeping an eye out for your stamina. When you see his swords light up, listen for two very heavy quicksteps. You will hear one quickstep followed by the second one, as soon as you would hear the third quickstep, hit the parry button and riposte. Stand in front of him, lock on and hit him two times with your weapon.
At this point, he will dash away and either do a thrust attack followed by a slash or a quick slash. This is the quick slash version, to parry it, wait for his sword swings and reach the 10 o’ clock of your screen and hit the parry button. Riposte and get behind him. At this point you should be able to finish him off, if he starts the transformation, back away and finish him off after the transformation is completed. And there you go, dead.
I will show you how to do this again and how to deal with the thrust + slash attack. Do the same thing, listen for the two quicksteps, hit the parry button as soon as you would hear the third quickstep. Parry. Riposte. Lock on and hit him two times. Wait for the thrust and roll backwards. Hit the parry button immediately after you recover. Riposte and get behind him. Finish him off. And he’s dead. Thanks for watching! .
As found on Youtube