Cleon
Legend
I suppose the hp loss could work, although I'd favor this approach from other symbionts (replacing Int with Con in the example below):
Mind Feeding (Su): A cerebral hood survives by consuming its host's mental energy. This deals 1 point of Intelligence damage each day the hood remains attached. Ordinarily, the host regains 1 point of lost Intelligence each night, just before the cerebral hood drains a new point, keeping the host at an equilibrium point of -1 to its Intelligence. When the cerebral hood uses its mind blast, however, it deals extra Intelligence damage, so overuse of that special attack can eventually destroy the host's mind.
Don't mind the approach, but the implementation is a bit problematic. What's to stop the wearer using lesser restoration or the like to heal the ability damage? Wouldn't it be better as a penalty?