Thanks, everyone. I finally made it!

I raised my Pokemon to levels 59/60 and faced the Elite 4 and the champion. The POkemon I took with me were: Ditto, Charizard, Vaporeon, Snorlax, Steelix, Roserade. All EV-trained and Snorlax was supremely trained, whatever that means for the game.

I kept Dig on Steelix, but all she really had to do was use Iron Tail once. That was a 1HKO on the champion's most powerful Pokemon.

The one who did the most 1HKOs, however, was Vaporeon (6 times, including all 4 Fire Pokemon). I'm glad I took him with me.

(Spoiler:) My only regret is that none of my Pokemon got experience from defeating Tyrantrum, since he knocked out my Charizard with Head Smash and knocked itself out from the recoil. But that was the only time one of my Pokemon fainted, so all things considered it was much easier than I had expected.

The only annoying part was (Spoiler:) Drasna's Altaria with its incessant singing. By the way, (Spoiler:) am I the only one who finds Drasna really creepy? She looks like the kind of character whose favorite meal is little children.