One of the most important things I've found with boney.....is to joust it.
Dont treat it like a peerless, i.e. depend on your life leeching, mana leeching abilities to do everything. He can put out so much melee damage, that if your not healing, you'll be ooOOoOOOo'ing in no time.
Use a decent demon slayer, and as said before, fight him ALONE. Make sure even a patchwork is not around if you can help it. (dismounting f*(*$#!!'ers!)
When u need to, run away, and heal up. Use the tried and true method of jousting, and you'll get the hang of it.