It's the day after Pastoria City's Croagunk Festival—and while Team Rocket may have time to enjoy a leisurely marsh mud bath, Ash and his Pokémon must train for their Pastoria Gym battle. Buizel is so focused on victory that it loses its temper at Pikachu, then takes it out on Turtwig when the Grass-type Pokémon tries to play peacemaker. It's not a promising start to the morning but the Pastoria Gym Leader, Crasher Wake, is intrigued by Buizel's spirit; he shows Buizel his own Floatzel, capturing Buizel's interest.
Everyone moves to the Gym, where Crasher Wake welcomes Ash to the water-based battlefield for a three-on-three battle. For their first face-off, Crasher Wake chooses Gyarados and Ash chooses Pikachu. Pikachu's initial Electric attack doesn't faze Gyarados, but a mid-air Volt Tackle puts Gyarados down for the count. Next up is Crasher Wake's Quagsire, so Ash switches in Turtwig. Turtwig darts around the pool to throw off Quagsire, but Quagsire can still track Turtwig's every movement—Ash hastily withdraws Turtwig and sends out Buizel in its place.
Buizel is still annoyed with Pikachu, forcing Ash to call its attention back to the fight. Buizel turns Quagsire's Ice Beam attack into a frozen Aqua Jet combo, knocking out Quagsire, and Buizel's real opponent enters the ring: Floatzel! Floatzel takes everything Buizel can dish out and comes back for more, using its flotation collar to help absorb incoming attacks. Then, confused by its own attack, Buizel is forced to take a break while Pikachu subs in, but Floatzel soon has Pikachu on the ropes. Buizel recovers and takes over the fight, giving Pikachu a high-five, and knocks out Floatzel with an aerial Water Pulse. With that, Ash's team scores a clear victory earning him a brand-new Fen Badge!
Team Rocket is relaxing in the Great Marsh. Meowth doesn't want to get in the marsh, but James and Carnivine pull him in, having him land on his face.
Meanwhile, outside of the Pokémon Center, Buizel is training hard for the next Gym match, eager to make up for only managing a draw against Maylene's Lucario. Ash is also in the mood for serious training and he and Dawn agree to have a training match. Piplup starts things off with Whirlpool and Pikachu responds with Iron Tail. Pikachu uses Thunderbolt but Piplup dodges and it accidentally hits Buizel. Buizel isn't very happy about being shocked by his teammate and tries to pick a fight with Pikachu but Turtwig intervenes and tries to push Buizel back. Turtwig tries too hard and makes Buizel fall on its back. Buizel, now very angry with both Pikachu and Turtwig, uses Sonic Boom but Ash gets in the way, taking the blow. Crasher Wake, having come by to make sure that the gang aren't too worn out by the previous evening's celebration, notices Buizel's behavior. He sends out his Floatzel which looks down on Buizel. Ash checks Floatzel on his Pokédex, and finds out that Floatzel is the evolved form of Buizel.
Ash and Crasher Wake are in the Gym field and the judge is explaining the rules. Crasher Wake sends out his Gyarados and Ash sends out Pikachu. Pikachu makes the first move with Thunderbolt which hits Gyarados, and it appears that it's going to take serious damage. However, Gyarados seems hardly phased; it charges up and uses Dragon Rage. Pikachu counters with Iron Tail and the overhand strike allows him to soar into the air, reaching apex right above Gyarados. Gyarados goes for Pikachu with Bite but to Crasher Wake's surprise as Pikachu falls, Ash has him use his growing momentum to go into Volt Tackle. Pikachu collides into Gyarados' face and Pikachu stands out as the winner.
Crasher Wake sends out Quagsire and Dawn checks it out on her Pokédex. Ash calls back Pikachu and sends out Turtwig. Turtwig uses Energy Ball but Quagsire uses its slim body to dodge into the water. Turtwig jumps over the panels on the water and Crasher Wake notices how fast Turtwig is. After watching Turtwig's jumps causing tell-tale ripples from panel to panel, Quagsire uses Sludge Bomb and sends Turtwig flying backwards. Quagsire jumps up and uses Ice Beam. After initializing an Ice Beam, Quagsire uses Sludge Bomb but Ash calls back Turtwig. Ash sends out Buizel and uses Sonic Boom. Quagsire seems to not have even felt the attack and Quagsire charges up for Ice Beam. Remembering the combination they used in the Wallace Cup, Buizel uses Aqua Jet as Quagsire releases the Ice Beam. Buizel goes head on towards the Ice Beam and is able to create Ice Aqua Jet which strikes Quagsire directly knocking it out.
Crasher Wake sends out Floatzel and Buizel charges with Aqua Jet. Floatzel inflates its sac and deflects Buizel's attack. Buizel uses Water Pulse but Floatzel blocks it by merely punching it. Floatzel uses Razor Wind and Buizel is thrown into the water. Buizel gets out and uses Water Gun but Floatzel blocks with its left fin. Buizel charges at Floatzel but Floatzel dodges and punches it into the water. Floatzel uses Bulk Up and swims after Buizel. Buizel uses Sonic Boom and Floatzel uses Razor Wind. Buizel continues to swim away but Floatzel is gaining up on it. Ash calls out for Buizel to think of the water as its friend. As Floatzel gets closer, Buizel inflates its sack, stopping suddenly while Floatzel zooms ahead. Buizel scores a direct hit at Floatzel's exposed back with Aqua Jet. Then, Buizel uses Water Pulse and a geyser of water is pulled upwards with the attack, pinning Floatzel against the Gym ceiling. Floatzel uses Ice Fang to get out of it and Buizel uses Sonic Boom. Floatzel dodges and uses Ice Fang. Buizel bites the Ice Fang after it hits and uses Water Pulse. Floatzel inflates its sac and sends the Water Pulse back at Buizel. Buizel gets knocked back and is confused.
Floatzel uses Razor Wind and Buizel tries to use Aqua Jet but only turns around. Buizel gets knocked towards Ash and Ash decides to send out Pikachu. Pikachu uses Thunderbolt and Floatzel uses Whirlpool. The attacks collide and electrified droplets of water fall, shocking Buizel out of its confusion. Pikachu uses Volt Tackle but Floatzel stops that with Razor Wind, sending him flying in the air. Floatzel jumps up and uses Ice Fang. Pikachu falls backwards and recovers a little bit after the attack only to find out that Ice Fang froze part of his back. Buizel, having watched Pikachu give his all in spite of the difficultly he's having, wants to battle now and Ash sends it out. As Pikachu and Buizel pass each other, they high-five and Buizel uses Water Gun to break the ice off Pikachu's back. Buizel jumps and uses Aqua Jet and Floatzel uses Ice Fang. Both Pokémon fall back to their places and Floatzel uses Razor Wind. Razor Wind hits and creates a cloud of smoke. Floatzel jumps up but as the smoke clears, Buizel is nowhere to be found. Buizel jumps up from out of the water and releases a Water Pulse at point blank range into Floatzel and sends Floatzel flying back. Floatzel is unable to battle and Ash has won the challenge.
Outside, Buizel and Pikachu make amends from the earlier incident and Crasher Wake gives Ash the Fen Badge. Ash does his pose and shows off his newly earned Badge. Meanwhile, at night, Team Rocket are sleeping in the Great Marsh and Wobbuffet is putting some mud on Jessie's sleeping eyes.