So yesterday I beat the game. :3
Blastoise with Surf and Ice Beam destroys 5/6 of the Champion's Pokemon.
And I've also been working on the post-game content. Other than finding the rest of the Megastones around Kalos, I believe I'm finished. Haven't used the Master Ball yet either, so it's nice to keep that around.
Right now I'm working on catching dittos so I can have an easier time with breeding (I caught 12 yesterday but the cartridge came out of the console