I just played through to Gomez twice, mapped out the entire mansion, revisited everyone/thing... but still couldn't figure out a way to beat him. I think that you're supposed to pick up a sword somewhere to duel with him. Maybe it's in the room before you actually fight him where he leaves you a heart?
The werewolf power up just gives you a second full bar of health.
Anyways, the final battle is in the room with those chains and thing is there too.