Expedition to Onix Island! (Japanese: イワークの島でサバイバル！ Survival on the Island of Onix!) is the 39th episode of Pokémon: BW Rival Destinies.
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? And will Dawn's Piplup and Ash's Oshawott ever get along instead of fighting over for Meloetta since she comes along?
Ash has Oshawott use Water Gun on a target for training. Meloetta watches them, while Iris has Excadrill and Axew fight each other. Cilan plans as well for Pansage, while Piplup comes with a tube, wanting to swim. Dawn proposes to relax a bit, as she proposing to go on a deserted island not far from here. Iris and Cilan agree, but Ash does not want to, for he needs to train. Dawn replies the island is special, for Onix live there. Ash is interested and Dawn remembers there are stories if one defeats the special Onix, something amazing will happen. They come to Jervis, who tells they will travel by boat. Ash is psyched, but Iris replies he is a kid, with Dawn thinking he may go overboard. Meloetta appears and Ash asks her to come with them, while Piplup and Oshawott continue their rivalry.
They ask Jervis for specific info about Onix, but he knows only that if one sees the special Onix, they will get lucky. Team Rocket flies in helicopter, going to a location. After arriving on the island, the Pokémon come out and run off. Before leaving Jervis asks of the heroes to be careful, then rides off, promising to pick them up before dinner time. As the Pokémon play, Oshawott gets gripped by Krabby and Piplup is chased by a Kingler. Ash becomes hungry, so Cilan decides to make lunch, while the rest have fun on the beach: Ash dives, Iris and Dawn play in sea, while Oshawott and Piplup bicker about Meloetta. Later, the heroes have lunch and Dawn admits he is an awesome cook like Brock. Ash explains to Iris and Cilan Brock was a friend he travelled with in the past.
Oshawott and Piplup offer their own food to Meloetta. However, they start to fight, so Pansage, Pikachu and Axew restrain them. With the meal over, they go to visit the special Onix. They are in front of the cave, where Ash believes Onix live in. Iris and Dawn reply it is not always true, thinking he is a kid to suppose everything. Ash enters, but is startled by Woobat. Dawn and Iris humiliate him and enter. They notice the cave is very large, so they suspect the Onix are far larger than they anticipated. The cave begins to shake, as an Onix appears, so the heroes try to run out. After some encounters with Onix, Iris, Dawn and Axew come out. Dawn notices Piplup is gone, so they return back, but run once more after seeing the Onix again. Dawn proposes to go back to the beach, for the special Onix may find them instead.
Ash and Cilan see Iris and Dawn are gone. Piplup is depressed, so Oshawott tries to comfort him, but they start their rivalry once more. Ash thinks they should go back to the cave to find the girls, as well as the special Onix. Cilan disagrees, thinking it would be wiser to get back to the beach to make a new plan. As they go, an Onix appears. Oshawott uses Water Gun and Piplup Bubblebeam, causing Onix to retreat. Ash praises them both, who annoy each other. They turn around, but notice Meloetta has vanished, while more Onix appear. Ash has Piplup and Oshawott use Bubblebeam and Water Gun, but they miss. Onix attack, but Meloetta sooths them with her voice. She sings a song and changes her form. Using Close Combat, she causes the Onix to retreat, then shifts back into her normal form. Ash thanks her, while Oshawott and Piplup like her even more.
Dawn and Iris reach the bottom of the cliffs. They point to a path, though Dawn has a hunch her path is better. They go to Dawn's path, but reach another dead end. They try Iris' path, but reach another dead end. Iris finds a Magnemite, but gets shocked by it, while Dawn gets paralyzed by Foongus' Stun Spore. Later, they swing the vines. Dawn is shocked, but manages to get a control of it. The vine breaks, however, though Iris lands swiftly, while Dawn lands in a bush. They encounter an Onix and run away from it. Meanwhile, Cilan and Ash come to a dead end, but notice the strange rocks. Pikachu touches them, but these are actually Onix, who chase them away. They soon meet up with Iris and Dawn, but come to a dead end.
Oshawott uses Water Gun and Piplup Bubblebeam on Onix. Oshawott uses Aqua Jet and Piplup Headbutt to attack the Onix. Meloetta is in trouble, so the duo intensifies their attacks: Oshawott uses Hydro Pump and Piplup Water Pulse. The heroes are overwhelmed, so Ash asks Meloetta to sing the song. She does so, though the Onix still attack. However, they hear a roar and look up and see a shiny Onix, who calls off the attacks. All Onix, including the shiny, leave the heroes. The heroes think they may have a good luck for the Cup, or at least for some other things.
Later, Jervis takes them back to the house, telling they shouldn't have entered the cave. He claims he did warn them to be careful. Cilan wonders why Onix called off the attack, so Jervis suspects Meloetta's song caused its heart to be touched and called the attack off. A Wailord jumps and dives into the sea, with the water splashing, causing a rainbow to appear. Oshawott and Piplup try to get Meloetta's favor, but they fight, making Meloetta amused. Meloetta sings the song, so everyone thinks of their home. Jervis admits Meloetta's song has some mysterious power. Meanwhile, Team Rocket drops a machine, as they intend to find some ruins below the sea, while they allow the twerps to do their work for them.
Meloetta (Pirouette Form)
The "Who's That Pokémon?" is Onix.