Well, the thing with /zero Caster is that I'm not sure he, personally, is that hard to deal with since he was improperly summoned, it's more what he summons himself.

Also if he was actually here I don't see him lasting long at all since he's Gilles de Rais post-insanity and is therefore a gleeful child murderer. Like I don't think he'd last more than a few minutes.