Vampirism

I see that it lets you drain HPs with unarmed combat attacks , does it have any negative effects?

It slowly lowers Wis.

got it. Does the energy drain effect work with the beast claw, since it trains unarmed combat?

Hmm, I think you've got to be not wielding anything, otherwise it will revert to the weapon.

Does the status persist when mirrored in Sumos ring?