Overall, I really enjoyed this episode. Iris' return as a Champion, her Axew evolved into Haxorus, Dragonite being in sync with her, Claire and Cilan's flashbacks.
I think the episode did a good job at starting the battle as soon as possible. I would have loved to know with a bit more detail exactly what Iris did to become Champion, who did she defeat, etc. But it's fine, they didn't have that much time to work with.
Dracovish surprising Iris and Dragonite makes sense. And Ash's Dragonite is clearly a powerhouse, he takes hits like a beast. Reminds me of Ash's Snorlax.
Dragonite using Hurricane as a counter shield was great, and learning Draco Meteor to defeat Haxorus was a nice touch. I specially like Iris and Ash's Dragonite's interactions. Dragonite grew up a lot during this fight, Ash has to thank Iris for upgrading his Hug n' Kill Machine.
I imagine Dragonite's moveset right now is: Dragon Dance, Dragon Claw, Hurricane and Draco Meteor. Hyper Beam is probably gone. Funny thing is, we never really got to see Hyper Beam being shot. Both times Ash commanded it, Mega Lucario and then Iris' Dragonite stopped the attack before it was fully charged.
Its simple, recall in 4th generation where Infernape learned flare blitz as an upgrade to flame wheel
Also Pikachu learned Electro Ball in BW in a situational way, but then was able to use it at will.