SM043

When Regions Collide! (Japanese: ジムバトル！Ｚワザ対メガシンカ！！ Gym Battle! Z-Move VS Mega Evolution!!) is the 43rd episode of the, and the 982nd episode of the Pokémon anime. It first aired in Japan on September 21, 2017 and in the United States on December 9, 2017.

Blurb
Our heroes visit the Cerulean Gym, where the Alola students get their first taste of a Gym battle! Mallow and Lana challenge Misty, who praises their battle instincts after her victory. Next, Sophocles and Lillie face Brock and his Geodude—and Sophocles forgets that the Kanto Geodude is a Ground type, so his Electric-type moves won’t work!

Kiawe’s Turtonator goes up against Brock’s Steelix, and both Trainers show their full power as Steelix Mega Evolves and Turtonator uses a Z-Move. Finally, it’s Ash and Pikachu vs. Misty and Gyarados, just like old times! Misty also uses Mega Evolution, but Pikachu’s Z-Move manages to take down the mighty Mega Gyarados!

Plot
As a part of their extracurricular lesson in Kanto, and  from Pokémon School have arrived at the Cerulean Gym to learn about Gym s. Upon entering the Gym, the group notices something standing in the middle of the battlefield, which Ash quickly recognizes as. thanks Psyduck for looking after the Gym while she was away, and then properly welcomes Ash's class to her Gym. While and  exchange high-fives with Psyduck, Ash can barely contain his excitement. properly introduces Misty as the Gym Leader of the Cerulean Gym and  as the former  Gym Leader of the Pewter Gym. With the formalities over with, Kukui tells everybody to have some intense battles.

Kukui proceeds to explain how in Kanto, a Pokémon Trainer can travel from Gym to Gym to challenge Gym Leaders, and, if victorious against one, will earn that Gym's respective Badge. To demonstrate, Misty and Brock introduce their respective Gym Badges, the and the. asks Ash if he collected all the Badges in Kanto, which Ash confirms. However, Misty and Brock remind him that he got their Badges out of pity, causing his classmates to look at him questioningly. To avoid answering, Ash takes a few steps back and changes the subject, mentioning how Trainers with eight Badges are allowed to challenge the Pokémon League. With the embarrassing question avoided, Ash steps back forward and explains that the Pokémon League is a battle tournament full of strong Trainers. When Kukui asks who wants to battle Brock or Misty, everybody raises their hands. With everybody throwing suggestions who they want to battle, Misty decides to organize Multi Battles, allowing them all to have battles against them. First, and  team up against Misty, with  and  facing Psyduck. As starts recording the battle, Mallow kicks things off with, which successfully hits Psyduck. Lana continues by having Popplio use, which also hits. Misty counterattacks by having Psyduck use, but Popplio creates a balloon, which absorbs the Water-type move. Popplio the launches the balloon at Psyduck, who gets trapped inside the water-filled bubble. Misty mentions that her Psyduck is strong when in a pinch and orders a, but nothing happened. Ash, unsurprised, explains how Misty's Psyduck is a bit slow. Mallow has Steenee use Magical Leaf again, which bursts the balloon and causes Psyduck to fall on its head. Misty, knowing that the ensuing headache will allow Psyduck to unleash its hidden Psychic potential, isn't worried at all. And indeed, Psyduck then proceeds to hurl Steenee and Popplio into the air with Confusion. However, before anything else can happen, Misty tells Psyduck to bring Steenee and Popplio back down, and Kukui declares the battle being over. As Misty compliments Mallow and Lana, Psyduck finally registers the impact on its head, flailing in pain. While Rotom and Mallow sweatdrop, both Lana and Misty admire Psyduck's cuteness, with Misty even proceeding to hug it.

Next up are 's and 's Snowy against Brock's Geodude. Sophocles starts the battle with a, which however, much to Sophocles's shock, is completely ineffective against the Rock Pokémon. Brock explains that while may be a Rock/Electric type, Kantonian Geodude is Rock/Ground, making Electric attacks useless against it. While Sophocles feels embarrassed for having forgotten about regional variants, Lillie has Snowy attack with. However, Geodude uses, deflecting the attack. Sophocles is surprised to see Gyro Ball being used as a defensive move, and Brock explains that a "certain challenger of his" taught him how to battle like that, looking at Ash in the stands. Kukui then comments how these battles demonstrate the fact that a Pokémon's type, moves, and the way it's raised can create infinite new ways to battle. Sophocles admits that knowing the opponent is important to avoid making mistakes like the one he just did. With Kiawe and Ash's turn coming up, Kiawe requests to have a serious battle against Brock, while Ash wants to have a similar battle with Misty. Pleased by this unexpected turn, Kukui tells them to not hold back.

The first serious battle takes place between Brock and Kiawe, with Misty working as the referee. She declares that the battle will be one-on-one, with the battle being over once one side's Pokémon is unable to battle. Declaring his confidence in his battling skills, Kiawe sends out, while Brock sends out his own partner,. While Rotom gives Steelix's Pokédex entry, Sophocles deduces that as a Fire type, Turtonator has an advantage over its opponent. However, Lillie reminds him that Steelix is also a Ground type, making the odds fifty-fifty typewise. Kiawe begins the battle with, which makes direct contact. However, Brock has Steelix use Gyro Ball, repeating his deflecting tactic from before with Geodude to repel the flames. He then has Steelix use, but even when binded, Turtonator is able to use , causing Steelix to be blasted away from it. Kiawe then has Turtonator use, but Steelix avoids the attack with , seconds later launching its own counterattack against the Blast Turtle Pokémon. Knowing that dragging the battle on won't do them any good, Kiawe decides to use his Z-Move to finish the battle immediately. Brock, however, having heard of Z-Moves, decides to go all out himself as well, pulling off his shirt and revealing a necklace with a Key Stone on it. He taps the stone, causing it and the Steelixite on Steelix's forehead to glow and making Steelix Mega Evolve into Mega Steelix, shocking Kiawe. In the stands, Kukui explains to Ash's classmates that Mega Evolution is a phenomenon triggered by the bonds between a Pokémon and its Trainer, allowing it to power up mid-battle. Brock tells Kiawe to show him his Z-Move, which he starts performing immediately. With the poses done, the Z-Powered Turtonator fires its at Steelix, resulting in a huge explosion. However, as the smoke clears, Steelix is still standing, much to everybody's shock. Brock comments that the Z-Move certainly did its number on Steelix, but wasn't quite enough to finish the job. He then orders a from Steelix, and while Kiawe tries to counter it with Dragon Tail, the move still hits, causing Turtonator to faint and Kiawe lose the battle. Ash's classmates are shocked that Kiawe lost and marvel at the power of a Gym Leader. As Steelix returns to its normal form, Kukui explains that Mega-Evolved Pokémon return back to their normal states once the battle is over. Brock recalls Steelix and puts his shirt back on as Kiawe comforts Turtonator, only to be attacked by his, who's angry at them for losing.

While Ash's classmates express their excitement of having witnessed such a battle, Ash himself runs down to the battlefield to face Misty. Misty presses a button on a remote, causing the rocky field to sink into the floor, after which it's filled with water, creating a water field, leaving only some rock formations standing above the surface. Kiawe and Sophocles express their bafflement about Ash's excitement over the field change, which should put him at a disadvantage, but Ash assures them that he's alright. Unsurprisingly, Ash chooses to use Pikachu, while Misty sends out her as Brock takes his position as the new referee. Ash has Pikachu attack with, but Gyarados blocks the attack with. Misty comments how Water moves can be used to block Electric moves, confusing Rotom. Pikachu then charges in with, hitting Gyarados straight in the face. Ash tells Pikachu to follow up with, but while the attack is charging up, Misty has Gyarados use , causing a rainstorm to appear inside the Gym. As Pikachu launches his attack, Misty calls for a from Gyarados, which dissipates the Electric attack before it can hit the Atrocious Pokémon and blows Pikachu back in the process. Kukui admires Misty's strategy of using Hurricane in rain to shut down the Electric attacks that her Pokémon are weak against.

As Ash asks Pikachu if he's okay, Misty reveals her own Key Stone hanging on her hairband, causing Ash to flinch at the sight of another Key Stone owned by a friend of his. Bonding with the Gyaradosite on Gyarados's forehead, Misty's Key Stone triggers the Mega Evolution of her Gyarados, turning it into a Mega Gyarados. Ash smiles at the sight of this, and Misty has Gyarados attack with Hydro Pump, which sends Pikachu flying into the water below it. Gyarados follows up with, but Pikachu manages to get back onto a solid surface, allowing him to use his full maneuverability to avoid the attack. Ash tells Pikachu to use, which he manages to execute after climbing onto Gyarados's back, striking the massive Water Pokémon across the face and sending it underwater. Misty compliments Ash and Pikachu, before having Gyarados use Hurricane underwater, creating a cyclone of water around Pikachu. Pikachu tries to use Thunderbolt on the vortex, but the electricity just gets stuck on its sides. Misty comments that no challenger has ever been able to break her combination of Rain Dance and Hurricane. Ash, however, merely comments that breaking through stuff like this is what makes battles fun for him. To everybody's confusion, Ash tells Pikachu to climb out of the Hurricane, using Quick Attack to bounce off the electricity still circling on its sides. While everybody expresses their surprise of this unpredictable move, Ash and Pikachu begin performing their own Z-Move,. The devastating Electric attack is fired at Gyarados, who is unable to sustain the damage and faints, winning the battle for Ash. Misty compliments Ash of his increased strength, but also comments how he's still childish, irritating Ash. Meanwhile, the rest of the group is filled with excitement over these great battles, and Kukui tells everybody to remember what they experienced, even when they return to Alola.

At the airport, Brock and Misty hand Ash's class some replica Badges as commemorations of their battles, with all the girls getting Cascade Badge replicas and all the boys getting Boulder Badge replicas. Kiawe tells Brock that the next time they battle, he'll be earning a real Boulder Badge. Turning to and Samson Oak, Kukui says that this experience has given him confidence to realize his dream of making the Pokémon League culture take root in Alola as well. Brock and Misty approach Ash, telling him that they had fun during this reunion, it having reminded them of the old days when they used to travel together. Ash invites the two to come visit Alola sometime, and they gladly accept the offer. And while Ash's class flies back towards Alola, they're completely unaware of having secretly boarded their plane as well, riding on its tail.

Meanwhile, are also on their way back to Alola, still being carried there by, who apparently has been running on water nonstop for three days now.

Major events

 * and have a Multi Battle against, but the battle is called off.
 * Misty's Psyduck is revealed to have mastered.
 * and have a Multi Battle against, but the battle is called off.
 * Brock's Geodude is revealed to have learned and his  is revealed to have learned Gyro Ball and.
 * Brock and Misty are revealed to each have obtained a Key Stone, while Brock is revealed to have obtained a Steelixite and Misty is revealed to have obtained a Gyaradosite.
 * learn about Mega Evolution.
 * has a battle against Brock and loses.
 * has a battle against Misty and wins.
 * Misty's Gyarados is revealed to have learned, , and.
 * reveals that he intends to establish a Pokémon League in Alola.
 * Ash, his classmates, Professor Kukui, Samson Oak, and return to Alola.
 * follows Ash and his classmates to Alola on top of their plane.

Humans

 * Jessie
 * James
 * Samson Oak
 * Bystanders
 * Concetta (Poké Problem segment)
 * Sara Lee (Poké Problem segment)
 * Jessie
 * James
 * Samson Oak
 * Bystanders
 * Concetta (Poké Problem segment)
 * Sara Lee (Poké Problem segment)
 * Samson Oak
 * Bystanders
 * Concetta (Poké Problem segment)
 * Sara Lee (Poké Problem segment)

Pokémon
Who's That Pokémon?: (US and international),  (Japan)
 * (Mega Gyarados)
 * (Mega Steelix)
 * (Alola Form)
 * ('s; Alola Form; Snowy)
 * (Concetta's; Poké Problem segment)
 * (Sara Lee's; Poké Problem segment)
 * (Trainer's; Poké Problem segment)
 * (×3)
 * (×3; fantasy)
 * (Mega Steelix)
 * (Alola Form)
 * ('s; Alola Form; Snowy)
 * (Concetta's; Poké Problem segment)
 * (Sara Lee's; Poké Problem segment)
 * (Trainer's; Poké Problem segment)
 * (×3)
 * (×3; fantasy)
 * (Concetta's; Poké Problem segment)
 * (Sara Lee's; Poké Problem segment)
 * (Trainer's; Poké Problem segment)
 * (×3)
 * (×3; fantasy)
 * (×3)
 * (×3; fantasy)
 * (×3; fantasy)

Trivia

 * Poké Problem: Which Pokémon will battle in this episode?
 * Host:
 * Choices:, , ,
 * Answer: Gyarados
 * ,, , , , and narrate the preview for the next episode.
 * This and the previous episode feature thirteen main characters, the most amount in the entire.
 * A new Mega Evolution effect is introduced in this episode.
 * 's Steelixite and 's Gyaradosite are only visible when and  proceed to Mega Evolve their Pokémon.
 * This episode marks the first time that one (or more) main characters use Mega Evolution in the anime.
 * Brock uses Counter Shield in this episode, a tactic he learned from Ash during the.
 * This is the first time the Dare da? segment features a Mega Evolution.
 * When Brock and Misty Mega Evolve their Pokémon, they perform poses similar to the ones their game counterparts make in.
 * In addition, Brock taking his shirt off while doing this is another reference to Red and Blue, where his counterpart is also depicted without a shirt.
 * Both of them also recite their respective in-game Gym Leader slogans during their one-on-one battles.
 * Pokémon.com mistakenly stated that the episode would debut in the United States on December 2, 2017, which was one week before the actual US debut.
 * This is the season finale of Pokémon the Series: Sun & Moon.
 * The title card music from the is used as background music during Kiawe and Brock's battle.
 * Music from Volcanion and the Mechanical Marvel is used as background music.

Errors

 * When Ash mentions having won the Boulder and Cascade Badges, Brock and Misty slyly admit that they gave their respective Badges to Ash out of pity. While this was for the most part true with Brock, it was actually Misty's sisters who gave Ash the Cascade Badge out of pity.
 * In the dub,  states that Steelix is the Rock Snake Pokémon (the category of its ) instead of the Iron Snake Pokémon.

Dub edits

 * The Japanese text depicting and 's names are edited out in the dub.

In other languages
Wenn Regionen aufeinanderprallen! EP986 SL043 SM043 SM編第43話 精灵宝可梦 太阳＆月亮 第43集