That's just the gag of this series isn't it? having SO much power that he needs extra dice to do it 'properly'. lol

I wonder more how they manage to roll so many natural 20s...

they preroll dice and roll the ones that didn't roll high. It's the inverse of prerolling out 1's. It's what i use and how i end up with characters with nearly all 18's

I always got the feeling that Cory just had really good Dice. I have a set of ten D10s I call the Blue Soldiers, they've never failed to roll me awesome damage.
Best part is, their supernatural luck extends only to the players I actually like.