Ash and Goh travel back to the Sinnoh Region to attend a special festival celebrating the region's prehistory. Reuniting with Dawn and Cynthia, the duo's partaking in the festivities is cut short when a mysterious energy begins affecting all the Pokémon around Sinnoh. As their investigation leads them to Mount Coronet, and to their old friend Brock, Ash and company find themselves facing off against a reformed Team Galactic once more as they aim to reenact their plans to remake the world. But first, they need their old master, Cyrus, and they'll stop at nothing to get him back!
The special contains the following tropes:
- And the Adventure Continues: A variation. The special ends with a glimpse at the Hisui region, as Rei is shown catching Pokémon with his Oshawott, Cyndaquill, and Rowlett by his side.
- Ambiguous Situation:
- Goh wonders if Wyrdeer, Basculegion, the Hisuian Growlithe, and the Hisuian Braviary are still around for him to catch, but Cynthia never answers if that's still the case.
- It's not clear how Team Galactic escaped prison and reclaimed their Pokémon, nor how long they've been trying to bring back Cyrus. Considering they have a fully-operational base and laser cannon hiding at the foothills of Mount Coronet, they've been back for a while, but nothing regarding that is ever elaborated.
- Cyrus is still out there somewhere, but Team Galactic has no idea exactly where. Arceus knows, but it's not in a revealing mood.
- Ass Shove: Once the crisis has passed, Brock tries to ask Cynthia out. Cue Croagunk reenacting his famous Running Gag from Diamond and Pearl before dragging off his unconscious trainer.
- Beyond the Impossible: Ash, Dawn, and Goh use a combination of Dracovish, Piplup, and Inteleon's water attacks to try and cool off the rampaging Heatran. The fire proves so hot, it just makes Heatran even more powerful when it's hit.
- Breaking Old Trends:
- Ash temporarily catches a Rowlett, marking the first time he's caught a Pokémon he's already owned since his 30 Tauros. Averted for Dawn, who gets Oshawott rather than Cyndaquil, while the fire mouse ends up with Goh.
- Rei becomes the first main player character who appears without being one of Ash's friends (although there's a centuries-long difference in that regard).
- The Bus Came Back:
- The Magikarp Salesman makes a cameo in the background, marking the first time he's seen since Black and White.
- Team Galactic's lieutenants—Mars, Jupiter, and Saturn—along with their Purugly, Skuntank, and Toxicroak, mark their return to the anime after having originally been arrested towards the end of the Team Galactic arc in Diamond and Pearl. Azelf, Uxie, and Mespirit, who left after the end of the aforementioned arc, also make their return here.
- Brock rejoins the main group after his last appearance in Sun and Moon. Both his Croagunk and Chansey (now a Blissey), both of which were absent in the aforementioned series, also make their return alongside Steelix.
- Call-Back: Several to the Diamond and Pearl era, along with a few others:
- A non Diamond and Pearl one, but Piplup quickly starts butting heads with the Oshawott at the festival, much like it did with Ash's Oshawott during Dawn's guest appearance on Black and White.
- While investigating Mount Coronet, Ash and Dawn talk to Goh about how they stopped Team Galactic from capturing Dialga and Palkia so Cyrus could use the two to remake the world, and how he disappeared into the void of this world.
- Azelf, Uxie, and Mespirit call upon Ash, Dawn, Goh, and Brock to aid them in stopping the Team Galactic crisis, much as they did before during the last time the villains tried something like this.
- Croagunk pops out of its Poké Ball to battle Saturn's Toxicroak, his longtime rival. Naturally, he also stops Brock from asking Cynthia on a date via an Ass Shove, which Dawn lampshades that she hadn't seen in a while.
- After that scene, Ash and Dawn do their signature high five from the old series.
- Mars, Jupiter, and Saturn quickly recognize Ash, Dawn, and Brock for having defeated them originally.
- Brock mentions that the Sinnoh police should have disbanded Team Galactic, as they were working with Looker and the International Police to do just that.
- The Cameo: One of the booths at the Sinnoh Festival has the infamous Magikarp Salesman haggling in the background.
- Character Development: An offscreen variation. Brock has matured far more greatly now that he's gotten along further in his Pokémon doctor studies, especially when compared to his last appearance on Sun and Moon. He's not actively seeking out women like he was with Olivia, and when Cynthia does arrive, he puts off his attempted romanticizing until after the battle's clear and over (though it should be noted that in earlier seasons, whether he flirted at inopportune times was very much Depending on the Writer).
- Cool Ship: Brock has a medical craft that he uses to make house calls, and he proves to be handy to get his friends to Mount Coronet as quickly as possible.
- Continuity Nod: When the gang meets Brock, Goh mentions that Ash and Dawn spoke to him about their old friend before.
- Contrived Coincidence: Ash, Dawn, and Goh take an injured Chingling to a Pokémon Center to get it treated as the Mount Coronet crisis unfolds, and Brock happens to be there making the rounds. He even throws a lampshade about the odds of running into his old friends again at a time like this.
- Divine Intervention: Zig-Zagged. While Arceus does get involved with stopping Heatran's rampage, it leaves the rescuing of the Fire/Steel type to Ash and friends, as Cynthia points out, that it will help but it wants humanity to be able to solve its own problems.
- Forgot About His Powers: Brock doesn't think to Mega-Evolve Steelix to try and contain the rampaging Heatran, although given it has a type disadvantage, it wouldn't have made much of a difference.
- Mythology Gag: To Legends: Arceus and Diamond and Pearl:
- The entirety of the village seen at the Sinnoh Festival is an exact recreation of Jubilife Village.
- Basculegion, Wyrdeer, and the Hisuian forms of Braviary and Growlithe are seen in a painting.
- The old-school Poké Balls made out of wood are used in the catching game, with Ash, Dawn, and Goh surprised that they emit steam during the capture process.
- Oshawott, Cyndaquil, and Rowlett are seen as catchable Pokémon in the park, with Cynthia mentioning that those three were brought over from other regions during that time. She mentions that she was curious to see what impact it would have on the environment, referencing how their final evolutions would be regional variants thanks to the Hisuian environment.
- Cynthia brings out her Roserade, a key member of her team, for the first time.
- Arceus is seen using the Water Plate to give itself the water typing and contain the out-of-control Heatran. The plates are a key point in the post-game of Arceus's story and can be used on the Arceus in game once it's obtained.
- The crew unexpectedly encounters Cynthia by walking into a house, like the infamous moment in Pokémon Black and White.
- The Nameless: Wyrdeer and Basculegion are only referred to as the evolutions of Stantler and Basculin, and are never called by their proper names.
- One-Winged Angel: An unwilling variant. When Heatran absorbs the powers of the Fire Plate, it gets trapped into a giant form made of fire that destroys everything in its path without mercy. That fire then becomes molten lava, before it ends up looking like the Lava Titan from Hercules. Oh, and if it exploded, it would level the entire Sinnoh Region!
- Put on a Prison Bus: Cynthia has Roserade use Power Whip on Team Galactic, wrapping them up for the police to take them back to jail.
- Took a Level in Badass: Brock's Chansey is revealed to have evolved into Blissey, and learned Dazzling Gleam and Mega Punch.
- Truer to the Text: Mamoswine uses Ancient Power by stomping rocks out of the ground and flinging them unlike in Sinnoh where he shot a silver ball of energy.
- Vine Tentacles: Cynthia's Roserade knows Power Whip, which it uses to wrap Team Galactic up for the police.
- The Voiceless: Rei doesn't say anything during his cameo at the end.
- Walking Shirtless Scene: Brock rips off his shirt when the group tries to contain Heatran. He somehow gets it back when the crisis passes, and he begins to flirt with Cynthia.
- What Happened to the Mouse?: Though he's seen in the flashback, Charon, Team Galactic's chief scientist, is not seen with his teammates when they reunite, leaving it unclear where he wandered off to, or if he was arrested like the rest of them originally were.
