Well, it's a little thing called 'fair play', Kaiba. Ever heard of it?

"Delusion?" He shakes his head, with almost a pitying smile. "Didn't you hear? We all come from different worlds. Pokemon might not exist in your world, but that doesn't mean they're a delusion. I'd show you mine, but Pokeballs aren't working right now." Not that showing him would help much; he must have seen the Pokemon of the others by now, and another Dragonite wouldn't do anything more to convince him than the first one did.