Laurence, the First Vicar
You don't have to fight this beast to complete The Old Hunters, but if you've obtained Laurence's Skull, you can enter the chapel at the top of the Hunter's Nightmare and take him on. Laurence, the First Vicar won't be too happy to see you.
Remember the Cleric Beast? This fight is like that, but on steroids. Laurence uses simple swiping and slapping combos, best avoided by dodging directly under the claw to get behind him. The catch is that his attacks do heavy fire damage - you can be taken out with just two to three hits.
He may also slam his claw into the ground, getting it stuck. When this happens, back away or get behind him: he'll rip the claw free, causing fire to erupt around him. He may also leap into the air, either off screen or still in your field of view, so be ready to sidestep when he lands. This part of the fight really isn't too bad as long as you're smart with your dodges and attacks. He leaves himself wide open after most of this combos. And watch yourself when he falls over, as he will still flail around and try to attack you.
When his health hits about 40%, Laurence will topple over and lose his bottom half, forcing him to crawl around on his torso, fire leaking out behind him. This part of battle is very tricky. Dodging around him means taking damage from the fire, and he'll keep attacking with swipes. Your best bet is to chip away a hit or two at a time in between his swipes. He may slam his hands and crawl toward you, or spit up fire onto the ground. In both cases, you should just stay back.
Laurence might hit hard, but he leaves himself open for attacks. Keep pressing, and you'll be able to take down this twisted clergyman.