Interesting idea for a Master, and while he seems like a fun fellow to follow around on his shenanigans, I'm afraid my Saber is the picky type in regards to their Master, so I'll leave the choice up to random selection for now as to not resolve any potential conflict/friendships myself.

Oh, and a quick comment about your OC's Second Joker card, a field negating any and all magecraft while also acting as a numbing agent against Magic Circuits that lasts for several hours is a feat eclipsing the strength of Adra Castle, an entire building constructed to function as a mage's personal workshop capable of suppressing the magecraft of those within. That being said, a Workshop's main function isn't to crush or negate the magecraft of others as that is more of a secondary effect, and we've also seen cases of substances that can inhibit Magic Circuits upon contact, so I'm guessing such a powerful Mystic Code just might exist. It is highly specialized after all and only works for an instant. It is a scary trump card indeed, though it seems you've taken care to balance it appropriately.

By the way, just in case I came across as such, I don't really intend to scrutinize the ability, I actually think it's pretty sweet. It gives your OC the chance to reset the conditions of the battlefield and force everyone to calm down by de-powering all parties involved. It makes for a great show-stopper at a climactic moment while not granting him too overwhelming of an advantage since he'll be caught up in the effect as well. It's pretty neat.
That, and I'm a sucker for discussing abilities and powers, so please don't mind me fangasming... xD