The second phase of the boss just started and I also had hit it once. I think I spammed all the buttons to dodge the saws and the guy just got stuck on the saw with a ghost effect probably during the spinning animation (at least I think that's what the frame he was in was). The whole screen just froze in the middle of the fight and I don't know how that would happen considering I had already fought the boss a few times before (and lost). Nothing else moved and after some time the song stopped too.