I've seen lots of people complaining about the battle, which surprises me, because it was the best part of the episode in my opinion. Not only did we get to see that Blastoise is still crazy acrobatic after evolving, but it had a dance battle against Eevee! Now that's some smart thinking on the writers' part - establishing Eevee's dancing skill for Showcases by pitting it against an already-established character who excels at dancing (and in battle no less). I do feel a bit bad for Blastoise, though. While it's nice that it's learned new dancing tricks (like Tierno handstanding on Rapid Spin), I'm guessing it couldn't match Eevee's sheer nimbleness anymore due to its size. Really looking forward to a longer battle between Ash and Tierno (hopefully we'll get a proper one BEFORE the League as well), because it's awesome watching that Dance Battling. The fact they actually went the extra mile and included the rhythm strategy as part of Tierno's battles shows just how much dedication they have to the animation this time around, and the dynamic battles resulting from the strategy are among the most entertaining to watch.
Tierno's mention of losing at the Hyakokku Gym was also a good set-up. Was some decent characterization for Ash as well, considering he eventually withdrew his request for more info after Tierno starting talking, since he wanted the battle to be a surprise. While the Gym Leaders have virtually no story involvement compared to Generation V (which, as everyone knows, was a total missed opportunity on the writers' part), it's nice to see they're giving each Gym Leader at least one episode ahead of their Gym Battle for some characterization, and in this case, providing foreshadowing. Olympia's currently set up to be a much more imposing threat than she ever seemed to be in the games. Looking forward to how Ash'll overcome her Double Battle tactics. (Perhaps Thunder Armor?

I still remember that episode very vividly - it's ironic that the BREAK series in the TCG makes Pokemon look like they're all wearing Thunder Armor now. So maybe Frogadier and Talonflame BREAK? >_<)
Also interesting that Shauna's aware of Serena's feelings for Ash. Hopefully they do progress their (Serena and Ash's) relationship further than just playing this "Will they-won't they-probably not" game. At some point it better be Ash realizing something's up. He's more intelligent and observant than ever now, so it'd be well within his character to pick up on it eventually.