A Mudkip Mission (秘密の池！ミズゴロウがいっぱい！？ The Secret Pond! Full of Mudkip!) is the 25th episode of Pokémon: Advanced.
Get ready for a new episode of May's Expedition as she, Ash, Max and Brock stumble upon a swamp. There they find the swamp full on Mudkip and their caretaker, an elderly man named Old Man Swamp (or Mr. Swampy) who has the same whiskers as a Mudkip's fins. He explains that he gets Mudkip eggs from the Hoenn League and when they hatch they wait till their old enough to give to Professor Birch. But Team Rocket also has plans for the Mudkip. What evil will they have in store for them, and will Brock get a new friend?
May imagines herself leading an expedition near the river, as the heroes move onwards. Max suspects if they follow the river, they may find some rare Pokémon, while Ash hopes to find a spot for training. As the heroes continue on, they find themselves in a dead end, as they encounter a waterfall. Brock suspects this is where they can find the rare Pokémon. Brock throws rope and his Lotad uses Water Gun to push the rope, onto a tree atop the waterfall. May gets first and helps them, startling Ash how did she come here before them. May admits, as a "journalist", she had to be first, as she had Silcoon use String Shot to pull her up. The heroes see it is quite a damp, muddy area. The heroes encounter Mudkip, spotting some babies among them. May is happy she does not have one, as the last one attacked her, but seeing these babies, she changes her mind. May goes to catch one Mudkip, but one of them uses Water Gun, soaking her. One Mudkip falls into water and the current leads to the Waterfall, so Lotad goes to help it. Even Lotad can't get to shore, so another Mudkip, which soaked May, helps them.
Brock is amazed by the Mudkip and tries to befriend it. Ash, Max and May come to Brock, startling the Mudkip away. A man appears out of a bush, making May and Ash think it is a monster. The man mistakes them for stealing Mudkip he raised. Max explains they were just protecting the baby Mudkip, so the man calms down. The man introduces himself as Swampy. Ash tries to call him names, but drops the act. The heroes explain they climbed the waterfall so they can train, surprising Swampy. Swampy forgives them for trespassing, since they saved his Mudkip. At Swampy's lodge, the heroes have some tea. Brock spots some blue things, which Swampy describes as Mudkip eggs. Brock asks him where he got the eggs, so Swampy asks them why do Pokémon, who are to be chosen by a trainer at the start of the journey, raised at the same level. Ash and May have not given that much of a thought, so Swampy explains he raises the Pokémon to that level.
Swampy heard Professor Birch actually catches these Pokémon and raises them himself. Max wonders if this is breeding; Brock explains it is somewhat different of which he is working on. Hearing Brock is a Breeder, Swampy offers him to see Mudkip hatching from eggs. A Mudkip hatches from an egg; May is interested in it, but the Mudkip splashes May with water. Brock mentions he saw a large Mudkip, who helped Brock save another one back earlier. Swampy knows that Mudkip is a wild and bigger one, the one he didn't raise. Swampy worries all of that Mudkip's friends will leave and it won't have even a trainer to look up to. Team Rocket searches for twerps and stumble onto a fence. James explains that the fence protects something of value from the intruders. Seeing there could be something, James and Jessie bring Cacnea and Seviper out. Seviper uses Poison Tail, but with no effect. Cacnea uses Needle Arm, but it accidentally attacks James, making him bash through the fence. Wobbuffet gets out of the Poké Ball, causing it to hold a rope, Swampy hears the cans that have been tied to the rope, so he goes out to look. May, Ash and Max go with him, but Brock finds the Mudkip, who gets away, so Brock goes after it.
Brock finds the Mudkip and offers it some food, but it refuses to eat. Swampy, May, Ash and Max come to the fence, finding it destroyed and the cans stomped. Team Rocket appears and chants their motto. Swampy accidentally tells Mudkip are rare and that if the dam were to break, the Mudkip would be washed off into the river. James sends Cacnea, who uses Needle Arm, but on James. James is thrown against the dam, opening a hole in it. Brock is still offering food to Mudkip, but he sees a giant wave coming. Brock sends Forretress, who uses Rapid Spin to stop the wave. Lotad brings the baby Mudkip to the shore and Brock and the larger Mudkip the other ones. With everyone secured, Brock leads everyone up, to a higher ground, where the wave won't hit them. Brock praises everyone, but spots one lone Mudkip left. The larger Mudkip gets the smaller one, but the stream is strong, making it go to the waterfall. They fall, but are left hanging on a rock on a waterfall.
Brock ties himself with the rope they used to climb the waterfall, then dives in and goes to Mudkip. Brock reminds Mudkip it will fall down if it does not come with Brock up. Mudkip hesitates, but shows its tail and Brock pulls them to himself. The heroes pull Brock upwards and rescue them. However, more trouble arises as Team Rocket starts cutting the trees and steals the Mudkip in their machine. Brock remembers that the ground is quite soft and orders Mudkip and Lotad to use Water Gun to soften the ground even more. Team Rocket laughs, but their machine is sinking into the earth. Mudkip tackles the bag, freeing Mudkip, allowing Pikachu to use Thunderbolt to blast Team Rocket away. Brock thanks Mudkip for the assistance, while Swampy proposes Brock should take Mudkip, as Mudkip really likes Brock. Brock asks Mudkip would it come with him, but Mudkip hesitates. However, Brock convinces Mudkip, who is happy to go with Brock as its new friend.
- As of this episode, Brock, May and Ash own all three of Hoenn's Starter Pokémon: Torchic, Mudkip and Treecko.
- Featured Pokémon: Pelipper
- James quoted about "It's all well that ends well!" A reference for breaking their fourth wall in the end of the episode Wherefore Art Thou Pokémon!. This also applies to Meowth when he stole James' lines from his quote after they were blasted off from Ash's Pikachu's Thunderbolt.
- Old Man Swamp is revealed for breaking his own secrets which it was seen in this episode.