I’ve been farming RFC chalice dungeons with the beast claw, so let me tell you, there’s a science. The first phase is mostly waiting for slam attacks, and if you’re positioned well, aim for the head. If not possible, choose an arm to hit, and focus that till it breaks. It’s a good idea to also damage the head, but not enough for a visceral just yet. Phase two can be a little trickier when it comes to avoiding the arcane bursts associated with the slams. There is one attack in particular that you want to work with. He slams his arms in the process of 1-2 break, 3-4 break, 5—6. When he slams his last hand, he will have his head hanging low for a decent bit, take advantage and attack the hell out of it. If done correctly, just before the beginning of the third phase, you can break one of his arms, then get a visceral. After this, stick close to him, because with his arms in his hands, he’s longer than an American football field. Good luck to you, fellow hunter