A relaxing day at the beach, fun in the sun, and a whole horde of Onix! Just as Ash and co. are spending their time to have fun and start their Expedition on Onix Island after they arrive here turns out to be a quest for survival as they try to avoid one Onix attack after another. The worst part is Iris, Dawn and Axew are separated for the group when they ran away in opposite directions trying to get out of the cave. Will they find the guys again and get out of here? Yes. But when they are seperated they get attacked by Onix! And will Dawn's Piplup and Ash's Oshawott ever get along instead of fighting over for Meloetta since she comes along? Yes.
When Ash told Oshawott that his Water Gun needs more power than that if they're going to win the Junior Cup, Hydro Pump would've been much stronger than Water Gun since they haven't master it in training.
At first, Bianca told Ash's Oshawott to use Hydro Pump once, but he hasn't learn it yet in BW013: Minccino-Neat and Tidy!, but until 76 episodes later, he did learn it while taking out waves of Onix with Piplup in order to protect Meloetta.
It also reflects on how Ash will use his Pokedex to scan the same pokemon in each gen.
Meloetta changes into her Piroutte Form for the first time making this the first time in the anime to show both of Meloetta's forms.