Well I did finally manage to nail him. I had a save just before the fight and used that as each time he seemed to head straight for the wall and stand in between the two switches at the start of each fight. I was eventually lucky enough to flip both switches straight off and then join my creature and summond demon who already had him pinned up against the wall and together we beat him to death in about 5-7 seconds. It was still more down to luck than any kind of skill though. That even when you've flipped the switches he can just run past them and straight into his healing chambers doesn't seem right to me, especially when you then have to sit and watch helplessly as he runs from one chamber to the other to fully heal himself. If you could have flipped the levers to interupt his healing or intercepted him as he ran from one chamber to the other and caught him half healed, it would have at least given you a fair fighting chance. As it is, it is just a poorly designed and very frustrating and unfair boss fight.
I'm guessing the time when he "teleported" straight into a chamber from right in front of me when I had him pinned against the wall, is that one of the switches was probably not flipped, and it's probably slightly bugged so that no matter what you do, if one of the switches is still on then he'll always appear in a chamber for a heal. I say "teleported" but it was definitley bugged out as he dissapeared, he didn't run off or anything, and then I imediately got his healing cut scene.
