I just beat it today! And I used my Master Ball on Tyranitar. I got lucky with Metagross and caught him after a couple Ultra Balls and Timer Balls (I love Timer Balls, so many of these catching battles are wars of attrition for me), and I wanted Tyranatar out of the way so I could finish. Metagross' steel type makes chipping away at his HP easy, so long as he doesn't Shadow Rush. :P I admit I was in kind of a hurry to get through that part, though, because I'm playing alongside a friend so we can trade the females to our GBAs to breed, and this way we each have some the other doesn't have to trade. (Yeah, I know you could just restart before battles until you get all females, but that sounds too much like work for me. He did it on some of the later ones, though.) And we're meeting up to trade at Wizard World East in Philly this coming weekend, so I had to finish so I could get breeding!