The only way to fight him is to gain the dagger of extacyness and bring it with you when you pass out. Once you have met him face to face, you must them stab him through his 4th heart...IT MUST BE THE FOURTH HEART OR IT WILL NOT WORK. and then piss on him while his green blood bleeds him to death. Oh, and all this must be done while having sex with your sister, not your wife.
Please feel free to send me an update and let me know if you defeated him....I've been having the same problem.