I was able to steal his Extreme Shock during the first round but he used one against me a couple of rounds later. Does he have more than one or is this a bug?

it's quite possible he has more than one many opponents have more than one of each of their weapons

Ouch. Guess it's going to take a lot more for my pet to beat him 5 times.

Thanks for the reply!

no prob! i'm not sure if you're doing it already but you could try blasting his weapon(s) instead

I will! Thanks again. :)