I found a glitched death (I think at least.) When I killed him, he had a high pitched scream, instead of the low groan, it sounded like something that would be in his first phase. The most noticeable difference though was his pose when dying, his sword completely vanished and he went back into a pose similar to his first phase' posture, as in low to the ground, not standing up with his sword. He just kinda collapsed on the ground. He also didn't have the blood explosion on death like he/most beast bosses normally have. Maybe this was a death animation for his first phase that I somehow triggered? Maybe he was originally supposed to have two health bars, kinda like the Soul of Cinder in Dark Souls 3?