As Ash and his friends continue their journey to Sunyshore City, they are attacked by a wild Magnezone. As they reach a near-by town, they are informed by Officer Jenny that Magnezone and wild Metagross have suddenly appeared and is wreaking havoc throughout the town. As the group lead the Steel-types to the mountains using their Electric attacks, they meets up with Crispin, a mountain guard, who informs them that Magnezone and Metagross normally battle with each other on a regular basis to release the magnetism that builds up in their bodies, due to the strong magnetic forces emitted from the mountains. Recently, their battle arena (a deep crater) has become filled with water. Ash and co., Officer Jenny and Crispin have to find out why the crater is full of water, and a way to drain it, so Magnezone and Metagross can battle in peace away from the city.

After yet another failed attempt to master Draco Meteor, Ash's Gible falls into a lake and has to be saved by Buizel. After the successful rescue, Ash and Buizel are suddenly challenged to a battle by a Black Belt Trainer called Clayton against his Mr. Mime. Ash and Buizel naturally agree, however it soon emerges that this Mr. Mime is a powerful battler and Buizel is easily defeated. Determined to defeat this skilled Trainer and his Pokémon, Ash and Buizel combine their fighting spirits and train hard for the rematch. Ash wins the rematch, and Buizel learns Ice Punch in the process.

Ash and co. meet a man called Daniel, with a Snorlax who wishes to be the best at Pokéthlon. Ash competes with him and try to gain the title of Pokéthlon King.

The gang finally reach Daybreak Town in time for Dawn's next contest. After her last two losses, Dawn is eager to win her fifth and final ribbon. While there, she meets Ursula again who shows off her new Minun and Plusle, which brings up very uncomfortable memories for Dawn.

Dawn is quickly making her way to the finals, but Ursula is too. Their opponents one by one are being eliminated and the finals remain. Soon the finals pit Dawn and Ursula against each other. Dawn gets off to a good start with good combinations but Ursula's Pokémon have been well trained and prepared as Dawn's every moves are blocked. Eventually Dawn is able to make a comeback and finally earns her 5th ribbon. She is now confident to face many other coordinators that are participating in the Sinnoh Pokémon Grand Festival, held by Lake Valor. Now, they must journey to Sunyshore City Gym, to face Volkner and to claim Ash's eight and final badge.

With the contest over, Ash and friends head over to Sunyshore City. However, Ash's two rivals, Paul and Barry show up. During their meet, they understand through TV that there are only seven ribbons left. Later Barry asks Paul for a battle which he refuses. Instead, Barry and Ash have a battle, with Empoleon vs. Monferno. Monferno was struck by a Hydro Cannon which cause a rampage because its special ability Blaze, was activated, but when Team Rocket snatches Pikachu, Piplup, and Barry's Empoleon, Monferno finally controls his rampage at the last minute and evolves into Infernape. Paul does commend Ash for evolving his Monferno and tells Ash that for the next rematch, they will battle at the Sinnoh Pokémon League.

Ash brings out his Gible to train its Draco Meteor. However, every attempt by Gible falsely hits Piplup, who gets really angry and imagines how everyone will punish Gible and comfort him. Instead, Nobody is angry at Gible and don't consider Piplup's feelings. Devastated, Piplup decides to leave the group and return to Professor Rowan. Using this opportunity, Jessie and James plan to use Piplup to get Pikachu. In the end, everyone apologizes to Piplup, who has also learned Hydro Pump.

Ash and his friends have finally arrived in Sunyshore City where Ash is more eager than ever to battle for the final badge he needs to qualify for the Sinnoh League. The group immediately heads to the Gym, but are greeted by an unbelievable sight; a huge pile of badges is placed in front of the Gym so anyone can get one without battling. Ash, who believes that winning them with effort is what makes badges significant, is furious. He persistently tries to enter the Gym, but the high-tech Gym has a prepared machine which manages to capture him. Just then, a spark of light flashes and an Infernape appears, saving Ash from his troubling situation. It emerges that Infernape's trainer is none other than Flint, a member of the Elite Four who specializes in Fire-type Pokémon. Ash and co. soon discover that Volkner, Sunyshore's Gym Leader, is no longer interested in battling. Flint and Ash decide to battle each other to lift his spirits. Ash loses against Flint's Infernape, but is successful in motivating Volkner.

With Ash's battling style motivating Volkner, they are ready to battle, but their battle is interrupted by a power outage which is unusual in Sunyshore City as they have a well designed Power Tower; As they try to figure out what happened, the tower was launched up by Team Rocket. While Ash is battling Team Rocket, Grotle evolves into Torterra and learns Leaf Storm before blasting Team Rocket away. With Sunyshore Gym under repair Ash and Co. head towards Lake Valor.

With Ash's final gym match delayed, Ash and co. head towards Lake Valor for the Sinnoh Pokémon Grand Festival. They meet up with Dawn's mother, who asks them to help out at a school. Meanwhile, Jessie wins her fourth Ribbon at the Tonarino Town Contest.

Ash and company meet Marley, a young woman protecting a Shaymin sought by Team Rocket. They decide to help Marley search for the Gracidea flower needed for Shaymin's transformation to Sky Form, so that it can be set free safely.

Pokémon Ranger Ben meets the group while pursuing a wild Heatran, which has gone on a rampage. Team Rocket obtain Ben's Capture Styler and attempt to use it to capture Heatran for themselves.

Ash and his friends meet Elite Four member Bertha whom specializes in Ground Pokémon. Team Rocket as always tries to steal others Pokémon, this time from a young boy. Ash and team along with Bertha stops them. And as always, Ash is eager to battle her, and chooses Torterra against Bertha's Hippowdon, but quickly loses the battle.

Ash, Dawn, and Brock on their way to Lake Valor enter Arrowroot Town where a Pokémon Contest is about to start. They meet a Princess named Salvia and she wants to participate in the Araroot contest, so Dawn and the princess trade spots. Jessie battles Princess Salvia, who wins the ribbon but decides to give it to Jessie for her efforts. Thus Jessie earns her fifth ribbon and qualifies for the Sinnoh Pokémon Grand Festival, and Princess Salvia gave Togekiss to Dawn.

As the Team heads through the plains, its time for Dawn's practice with Togekiss for the Grand Festival. Togekiss is very much excited to show its elegance, but tries to showcase its look by taking hits of Gible's Attacks. Dawn tries to make Togekiss understand the battle styles with magnificent looks. The situation worsens when Team Rocket shows up, planning to steal Togekiss.

Ash and friends meet up with a trainer with two Dittos — one is normal, the other one is shiny — who asks Ash to battle her. Without much of Pokémon knowledge she makes the wrong choice of Pokémon in Ditto's transformation, Ash's Infernape beats her Ditto which transforms to Infernape, and Ash's Pikachu beats her other Ditto which transforms to Piplup and Pikachu. Brock helps her about the Ditto's transformation and knowledge on other Pokémon. Finally, the team arrives in Lake Valor for the Sinnoh Pokémon Grand Festival.

The team enters the Sinnoh Pokémon Grand Festival where Dawn meets Nando, Kenny, Ursula, Zoey and Jessie, who are also competing in the Grand Festival. During the First Round, Ursula uses two Eevees which have evolved into Flareon and Vaporeon, Nando uses Altaria and Kricketot, Zoey uses Gastrodon and Lumineon, Jessilina uses Seviper and Yanmega, Kenny uses Empoleon and Floatzel and the Festival continues with others. Kenny's performance is flawed when his Empoleon's Flash Cannon hits Floatzel's Whirlpool which knocks Floatzel down. At the end of the day, the results are announced except Kenny's. Dawn's rivals, including herself, makes it to the Battle Round. Kenny leaves Lake Valor to train even harder with his Pokémon.

The first contest battle begins between Ursula and Dawn. Ursula uses Gabite and Flareon. When Ursula is on the way to win, Dawn uses an Ice Chandelier combination, With only 7 seconds remaining, Dawn tells her Pokémon make the combination again and beat both Gabite and Flareon. Dawn makes it to the Top 16. At the end of the day, Zoey, Jessilina and Nando also move onto Top 16 in the Sinnoh Pokémon Grand Festival.

Dawn, Zoey, Jessilina and Nando are in the Top 4. The first battle for the day is Nando's Lopunny and Kricketune against Zoey's Leafeon and Mismagius. The second battle is Dawn versus Jessilina's Carnivine and Seviper. At the end of the battles the two coordinators who are in the Sinnoh Pokémon Grand Festival finals are Dawn and Zoey.

In the final round of the Sinnoh Pokémon Grand Festival, Dawn and Zoey battle begins. Zoey uses Glameow and Gallade, Dawn uses Piplup and Togekiss. During the battle Zoey uses Dawn's combinations to make her Pokémon powerful and beautiful. In the last seconds they both make a combination with their Pokémon. With a blinding light, the two combination attacks collide which causes a gigantic explosion that sends a strong gust of wind. Then they announce the winner who turns out to be not Dawn, but Zoey just by the smallest number of points. Zoey then hugs Glameow and Gallade. After the Sinnoh Pokémon Grand Festival is over, Nurse Joy tells Ash that Volkner is back and ready for a battle with him.

With the Grand Festival over, Ash and friends begin to head back to Sunyshore City for Ash's final Gym battle with Volkner. As usual, Team Rocket pursues them. But when Meowth falls in love with a Trainer's Glameow and decides to leave Team Rocket, Jessie and James enlist the help of Ash and friends to get Meowth back.

Ash battles Volkner for his last gym badge. Ash uses Torterra first, but it loses to Volkner's Electivire. Pikachu then defeats it. Next is Jolteon and Infernape and Infernape wins. Luxray is Volkner's last Pokémon and Ash sends out Pikachu again, but it loses. Infernape is Ash's final hope, but it gets hit one time after another. Being hurt badly Infernape's Blaze is then activated, but with Ash's friendship and trust on Infernape, it is able control it now. With one-after-another powerful attacks, Infernape keeps weakening Luxray. With a final powerful Flame Wheel attack Infernape beats Luxray giving Ash his 8th and final badge and enters the Sinnoh Pokémon League.

Having earned his final badge, it is time for Ash to head off to the Lily of the Valley Island for the Sinnoh Pokémon League Conference. However, as they leave Sunnyshore City, Ash & Co. meet both Dawn's rival, Kenny and their old friend Jasmine, the Gym leader of Olivine City in Johto. Kenny eagerly challenges Ash to a battle to which Ash accepts with the stipulation that should Kenny win, Dawn would agree to accompany him on a journey, just the two of them. In addition to that, Jasmine and Flint also have a training battle. Kenny wins his battle with Ash, but despite the outcome, Dawn turns down his offer and decides to follow a separate path after traveling with Ash to the Sinnoh Pokémon League.

On their way to the Sinnoh Pokémon League, Ash & Co. meet up with Flint's brother, Buck, a treasure hunter eager to find treasure on a nearby island. Buck requests the assistance of Ash & Co. in finding this treasure. However, Team Rocket also overhear this information and decide to get the treasure for themselves. Buck and co. find a ruin and a Claydol is guarding it. Buck catches the Claydol and the treasure turns out to be vases and other stuff.

It's almost time for the Sinnoh Pokémon League, and in training, Ash has decided to get all of his Reserved Pokémon together for some training and to decide who to use in the upcoming Sinnoh Pokémon League. However, when they arrive in Sinnoh, they all were released from their Poké Balls and are playing about nearby. To top it off, Team Rocket arrives with a dastardly scheme to capture all of Ash's Pokémon. But the Poké Balls get separated from Team Rocket when they're hit by Pikachu's Thunderbolt again, so Ash and co. searches and finds Totodile, Corphish, Snorlax and Bayleef. Cyndaquil is left, but Team Rocket finds it first. It then uses its new move Flame Wheel to crash into a tree and set it on fire. Ash and the others see the smoke and find it. They then destroy the machine but it fixes itself, and Team Rocket goes after Cyndaquil again. Just as they reach for it, Cyndaquil evolves into Quilava and learns ultra powerful Eruption to blast off Team Rocket. Afterwards, Glalie, Torkoal, Noctowl, Donphan and Muk show up so Ash can start his training session. At the Sinnoh Pokémon League, he sees that his rivals Barry, Conway, Nando, and Paul are all there. At last, the Sinnoh Pokémon League Tournament starts and Ash's first opponent will be Nando. Who will win?

Finally, it's time for the Sinnoh Pokémon League Lily of the Valley Conference. And Ash soon discovers that his preliminary battle in the First Round is against Nando – the Pokémon minstrel and the first trainer he befriended in Sinnoh. Ash decides to use his Quilava, Heracross and Staraptor, as Nando sends out Roserade, Kricketune and Armaldo. At first Nando takes the initiative, but later Ash grasps the situation gradually, by understanding Nando's style and rhythm. During the battle, Ash's Staraptor battled Nando's Roserade. After a few problems, Staraptor defeats Roserade, but is quickly defeated by his Armaldo. Quilava learns Aerial Ace and ends up fainting in a tie with Armaldo. Using Heracross against Nando's Kricketune, Ash defeats Nando, and moves on to his next match in the Second Round. Meanwhile, Barry, Conway and Paul also make it through the preliminaries. Meanwhile, talks of an incredibly powerful trainer with a Darkrai begin to stir up.

After Ash defeats his opponent in round 2, Paul, Barry, Conway also move to round 3. Ash discovers that his next opponent is Conway and that the upcoming battle is between Paul and Barry. Doing some research on their opponents, Ash, Barry and Paul each learn something about their opponents while Conway learns more about Tobias, who apparently managed to win all of his badges with just nothing but his Darkrai. When the battle between Barry and Paul begins, Paul's sends out his Magmortar, who easily defeats Barry's Skarmory after it using Spikes and because of Magmortar's power packed Flamethrower. Next, Barry send out Empoleon and Paul recalls it because of Magmortar suffer damage to Empoleon's strongest Hydro Cannon. Then, after a close battle, Paul's Ursaring defeats Barry's Hitmonlee, even though Hitmonlee got a powerful Blaze Kick, but Paul recalls Ursaring because of Empoleon seem to be to tough and sends out Electivire. After a fierce battle between Paul's Electivire and Empoleon with its special ability Torrent, which increases the strength of Water type moves when it has taken severe damage, but ends up fainting to Paul's Electivire, and so Barry is eliminated.

The next battle is between Ash and Conway. Ash's Infernape learns Flare Blitz and Gible masters his Draco Meteor. Originally, Ash was going to use Infernape, Torterra and Glalie but feeling power was not enough (and Conway was secretly looking at Ash's Team), Ash faces Conway with Noctowl, Gible and Donphan. Ash knocks out Conway's Shuckle with Gible and Lickilicky with Noctowl, but Conway's Dusknoir knocks out Noctowl and Donphan because of a move called Trick Room. With Gible and Dusknoir taken a lot of damage each, it looks as though neither side has the clear advantage until Gible bites through Dusknoir's Shadow Punch, unleashes Draco Meteor again, and knocks out Dusknoir with a well-aimed Dragon Pulse. Ash moves on, and enters in the Top 8 champions along with Paul, and Tobias. For the quarter-finals, Ash discovers that he will be battling Paul, during which Ash's Gliscor returns.

Ash and Paul are about to start their full battle and Ash decides to stick with the same team he had against Paul during there full battle at Lake Acuity. Paul chooses Aggron and Ash chooses Pikachu. After a fierce battle, Ash recalls Pikachu for Infernape who beats Aggron with a fast Mach Punch. Paul's next Pokémon is Gastrodon and Ash recalls Infernape for Staraptor. Staraptor hits Gastrodon with a Quick Attack. Paul surprises everyone by making Gastrodon do the Counter Shield with Muddy Water. Staraptor tries to hit Gastrodon with Aerial Ace but Gastrodon dodges it and hits Staraptor with a Body Slam. Gastrodon used Water Pulse and shot it up in the air to gain power when it hit Staraptor. Luckily it got out by using Close Combat on the floor. Ash recalls Staraptor because it took damage from Gastrodon's Ice Beam. Ash sends out Buizel and by taking Gastrodon's Ice Beam it did the Ice-Aqua Jet to Gastrodon. Gastrodon tries to hit Buizel with a Body Slam, but Buizel finishes Gastrodon with a powerful Ice Punch. Paul's next Pokémon is Drapion. It used Pin Missile on Buizel, who manages to block it with its Counter Shield. Drapion then used Cross Poison, but Buizel dodged it and did Sonicboom at Drapion's back. However, Drapion blocked it with its tail, and Drapion caught Buizel with its tail. Even though Ash is in the lead, Paul's Counter Attack has begun. Who will win?

Ash and Paul continue their full battle. Drapion managed to defeat both Buizel and Staraptor. Ash sends out Torterra and it did some damage to Drapion utilizing Energy Ball, Leaf Storm, and Rock Climb. But Drapion still manage to defeat Torterra even at a disadvantage. Paul recalls Drapion and send out Ninjask, while pointing out his real plan- sacrifice Aggron and Gastrodon to learn what Ash is using for his team. Ash sends out Gliscor. After a tough battle, Ash recalls Gliscor for Infernape. It used Flare Blitz on the underground to get rid of Toxic Spikes. Infernape finished Ninjask with a powerful Mach Punch. Paul's next Pokémon was Froslass and Ash recalls Infernape for Pikachu. After a tough battle, Pikachu beats Froslass with ultra powerful Volt Tackle. Paul send out Drapion and Ash recalls Pikachu for Gliscor. Both Ash and Paul are ready to battle to their fullest. For once, Paul does acknowledge Ash's worth as a trainer. However, who will win?

Gliscor manages to strike down with X-Scissor, but Drapion hits Gliscor with Pin Missile multiple times. Then, Gliscor dodges Cross Poison and burns Drapion with Fire Fang, finally defeating Drapion and leaving Paul with Electivire. Electivire uses Thunder on the ground and chunks of earth hit Gliscor, defeating him. Then, due to Electivire's immunity to Electric-type attacks, Pikachu falls in battle and is replaced by Infernape. Infernape and Electivire are at powerful clashes of ThunderPunch with Mach Punch, and Flamethrower and Thunder. Then, when Electivire grabs Infernape's arm, he inflicted a powerful Thunder attack, but is at a disadvantage when Infernape activates its signature trump ability - Blaze. Infernape charges with ultra powerful Flare Blitz and Electivire counterattacks with Giga Impact. Both Pokémon cause a huge explosion but Electivire is overwhelmed by Infernape's Flare Blitz (powered up by Blaze) and ultimately falls to Infernape due to the impact. Ash finally defeats Paul, and moves ahead, onto the semi-finals and enters in the Top 4 champions of the Sinnoh Pokémon League. Paul tells Ash that he is going to see Pyramid King Brandon and ask for a rematch, and they both agree to eventually battle again one day, with the hatred between them turning to friendship, as well as acknowledging Infernape's growth. Sinnoh Champion Cynthia says that, both Ash and Paul will be champions (like her) someday, and that she awaits that day. Ash's next opponent is revealed to be Tobias (the trainer with Darkrai). Will Ash manage to reach the finals?

After his big victory over Paul, Ash discovers that his next match is against the strongest contender in the entire Sinnoh Pokémon League, Tobias, who has easily won every battle, to reach the semifinals using only his Darkrai, who is able to easily take out Ash's Heracross, Torkoal and Gible using its Dark Void, Ice Beam, Dream Eater and Dark Pulse attacks. Ash brings out Sceptile, which manages to defeat Darkrai using Leaf Blade. This becomes the very first time for Tobias to have lost a single Pokémon, up to the semifinals in the Sinnoh Pokémon League. Tobias surprises everyone with his second Pokémon, Latios, who defeats Sceptile with Giga Impact. Ash sends out Swellow, only to be defeated by Latios's Luster Purge very quickly. Ash's final Pokémon is Pikachu. After a long battle, both Pikachu and Latios are declared unable to battle. With all 6 of his Pokémon eliminated, and being able to defeat only 2 of Tobias's Pokémon, Ash loses the battle. Tobias wins the final battle, with just Darkrai, wins the Sinnoh Pokémon League and becomes the Lily of the Valley Conference Winner. Elsewhere, Paul watches the battle on television and walks away saddened by the outcome.

On their way back to Twinleaf Town after the Sinnoh Pokémon League Lily of the Valley Conference over, Ash, Dawn, and Brock are to part ways soon. Meanwhile, being on a ship, Team Rocket, in a submarine enrage a group of Tentacruel. Team Rocket manages to come on the ship, which Ash, Brock, and Dawn are on. Due to this, before calming down, the Tentacruel badly poison 7 Pokémon on board. Nurse Joy was too far from the ship to be able to reach in time and help the sick Pokémon. With her not there, Brock tries to save them. Despite Team Rocket leaving only one Pecha Berry and with no poisoning antidotes, Brock, Ash, and Dawn don't give up. Asking other passengers on the ship, they are able to find 2 more Pecha Berries, some Heal Powder and a Lava Cookie is also given to them by an old female passenger. Brock makes medicine with the ingredients for the sick Pokémon. 6 of the Pokémon begin healing, but Pichu being harshly affected by the poison of the Tentacruel, the medicine is not able to help it heal. Brock makes an energy drink with some Oran and Durin Berries, but Pichu, although very sick, denies to take the drink. Happiny, not able to see Pichu suffering, evolves into Chansey and using the move Softboiled on Pichu, begins healing it. All the 7 Pokémon are eventually cured of their poisoning. When Nurse Joy reaches the ship, she tells Brock he can become a great Pokémon Doctor, if he wants to. Hearing this, Brock decides to change his goals and goes for his new dream, becoming a Pokémon Doctor.

The gang go their separate ways, but this proves to be too much for Piplup, so it runs away. Their Pokémon find Piplup, but Team Rocket catches them. Ash and his team save the Pokémon, making Team Rocket blasting off again. Dawn confronts Piplup and tells it that they have to depart and the team sees a battle between Cynthia and Flint, and Cynthia wins the battle. Ash decides to continue his journey to become a Pokémon Master, Brock wants to be Pokémon Doctor, and Dawn wants to be a Top Pokémon Coordinator. At the pier, Ash and Dawn exchange their final high five and Ash, Brock, and Pikachu say goodbye to Dawn and Piplup. As the ship departs, Ash yells out to cheer Dawn. Ash and Brock set off to Kanto and say goodbye to each other, with Brock turning towards Pewter City, and Ash and Pikachu returning to Pallet Town. They run the rest of the road, and at a new sunrise, bring their Sinnoh journey to an end and bringing up a new adventure in Unova region.

After concluding her journey with Ash and Brock, Dawn returns home and has to decide which of her Pokémon to take with her on her journey to become a Top Coordinator. The morning after, Johanna goes to Dawn's bed and tries to wake her up, only to find that Dawn had already woken up. Johanna goes outside to check if Dawn is there, and sees that Dawn is practicing with Cyndaquil. Cyndaquil uses a Swift and Flame Wheel combination which impresses Johanna.

After his journey with Ash and Dawn, Brock has returned home to Pewter City to take care of his siblings as well as studying towards gaining entry to a training school for Pokémon Doctors. Two of Brock's younger siblings come into his room and let him know that it is time for lunch. Brock gathers his siblings to the kitchen so that he can make them lunch, since their parents are away on yet another vacation.