Promoting Healthy Tangrowth! (Japanese: 森の王者！モジャンボ！！King of the Forest! Mojumbo!!) is the 134th episode of the Diamond & Pearl series, and the 600th episode of the Pokémon anime. It first aired in Japan on July 2, 2009 and in the United States on December 5, 2009.
The Lilypad Contest is coming up, and Dawn wants Mamoswine to learn some Contest moves. But Mamoswine doesn’t appreciate Piplup and Pikachu laughing as it tries to get things right! With its feelings hurt, Mamoswine charges off into the forest. Dawn follows it, and the two of them are gone for the longest time. Ash and Brock are about to look for their missing friends when they’re stopped by Verona, a forest ranger who forbids people from bringing Pokémon into the area.
Out in the forest, Dawn discovers the reason for Verona’s rule: a Tangrowth swings in and uses Absorb on Mamoswine, then leaves a Sitrus Berry as its calling card before escaping. This Tangrowth drains the energy of any Pokémon that enters the forest—the bigger the Pokémon, the better, but it’s just as happy to drain Meowth and Ash’s Grotle too!
Once Mamoswine sees Tangrowth again, it tries to pick a fight, but Tangrowth doesn’t want to battle. It’s not until Verona arrives with Ash and Brock that everyone realizes what’s happening: Tangrowth wants to save a dying tree that’s a key part of the forest. Tangrowth absorbs Pokémon energy and leaves berries to help them recover, then uses Growth to heal the tree. Unfortunately, the tree is still dying!
Team Rocket shows up to vacuum up Tangrowth and the other wild Pokémon, but Dawn and Mamoswine take out Team Rocket with Mamoswine’s new Hidden Power move. Once Team Rocket is gone, our heroes’ Pokémon offer to help Tangrowth and Verona identifies the spot where all the tree’s nutrients are stored. By using Growth on that spot, the tree is saved—and now Mamoswine has a great new move to use in the Contest!
Dawn decides to start trainingMamoswine for the Lilypad TownContest. She sends it out but it becomes uninterested and charges into a nearby tree. Following Brock suggestion, has Piplup demonstrate a Contest technique, and his Bubble Beam captivates Mamoswine's attention. Then Dawn suggests Mamoswine try a move. The Twin Tusk Pokémon uses Ice Shard towards the sky and shatters it with its tusks impressing everyone. Dawn calls for another Ice Shard, telling Mamoswine to spin and shatter it. Having never done this before, Mamoswine ends up breaking the Ice Shard on its head and two pieces of the ice get stuck in its nose, causing Pikachu and Piplup to start laughing. Mamoswine blows the pieces of ice out of its nose, but they bounce off a tree and hit it in the head, causing Pikachu and Piplup to laugh even harder. Irate, Mamoswine loses its temper and chases after the pair for laughing, only to be stopped by Dawn when they hide behind her. Feeling humiliated, Mamoswine runs off into a nearby forest. Dawn follows after it, while Ash scolds Pikachu and Piplup for making fun of Mamoswine while it was trying its best to get things right, causing the two to feel bad for their behavior.
Ash prepares to go in search of them but is stopped by Verona, a local Pokémon Ranger. Brock immediately falls in love with her, but Croagunk subdues him with a Poison Jab. She orders the boys to stay outside of the forest because of a dangerous wildTangrowth known for targeting large Pokémon. Hearing this, Ash and Brock fear for Dawn’s safety, so Verona agrees to help them with their search.
Meanwhile, Dawn soon locates Mamoswine. She tries to persuade it to come back with the promise of a Poffin snack. Before Mamoswine can agree, it spots something deep in the forest and keeps staring continuously there. Suddenly a Tangrowth appears and begins to attack them. Mamoswine tries to defend itself with Ice Shard. However, Tangrowth makes use of its forest surrounds by swinging from branch to branch to evade and land attacks on its opponent. Finally, Tangrowth uses Absorb on Mamoswine and drains all of its power then leaves. After its departure, Dawn notices it dropped a Sitrus Berry which Mamoswine eats, thus regaining its power. While Dawn wants to head back, she is forced to follow Mamoswine who is determined to get its revenge on Tangrowth.
Meanwhile, Team Rocket are stumbling through the forest in the hopes of food. They quickly forget their stomach grumbles when an Onix bursts from the ground. Tangrowth swings by and promptly drains Onix of its energy. Then as it leaves, Meowth notices that Tangrowth left behind a Sitrus Berry. After he picks it up, Tangrowth hears him and absorbs his powers too, making Meowth crumble to the ground dropping the Berry in Onix's mouth which instantly heals. Tangrowth leaves Meowth an Oran Berry, and quickly scoffs it down before his hungry teammates to regain his vitality. James and Jessie are impressed by Tangrowth’s power, and set their sights on nabbing it for Giovanni.
While searching for Mamoswine again, Dawn thinks she spots it in the bushes, but actually disturbs a feeding Ursaring. It proceeds to attack her with Hyper Beam. Thankfully, Mamoswine shows up knocking Ursaring with Take Down. Then it continues its search for the Tangrowth along with Dawn. Meanwhile, the search for Dawn is going nowhere, so Ash calls out Grotle for assistance. Tangrowth immediately arrives on the scene, and Verona warns Ash about its Absorb attack. Ash goes ahead and orders Grotle use Razor Leaf, but Tangrowth evades the attack by jumping from branch to branch. Grotle tries a Energy Ball this time, but Tangrowth dodges the attack and absorbs its vitality. Then it flees the scene again, leaving a Sitrus Berry behind. Instead of eating the Berry, Grotle uses Synthesis to heal itself. Verona is left wondering about Tangrowth's ambush attacks and the gifted Berries. Brock admits it doesn't need the energy for itself, otherwise it would eat one of the Berries. With the curiosity growing, Grotle picks up Tangrowth's trail and the group decides to follow.
Once night falls, Dawn finds herself lost in the forest along with Mamoswine. It sniffs Tangrowth's trail again and picks Dawn on its back then rapidly heading on Tangrowth's trail, where they meet other wild Grass-type Pokémon, a Bellsprout, a Cherrim, a Seedot and a Shroomish, which all proceed to stop them in their tracks. Cherrim hits them with Razor Leaf, Seedot with Bullet Seed and Bellsprout along with Shroomish both absorb Mamoswine's power. Afterwards Bellsprout offers it a Berry, but Mamoswine quickly recovers and charges ahead, scattering the Pokémon away. Mamoswine halts it advance at a giant tree, with Tangrowth and the other Grass types emerging from a tree hollow. Mamoswine insists on a rematch, stamping its foot in anger, though Tangrowth settles the situation with its words.
Ash, Brock, and Verona show up, relieved to see that Dawn is unharmed. They turn their attention to the giant tree, which Verona reveals is over 1000-years old. Closer inspection reveals that the tree is split in half, probably due to a recent thunderstorm, threatening the health of the entire forest. Tangrowth proceeds to use Growth on the tree, making the group realize its intentions all along. Then, the other Pokémon follow it with the same move but realize that there isn't enough energy in them. Verona pledges her assistance and Tangrowth is grateful for the offer. Suddenly Team Rocket shows up in their vacuum machine, sucking up all the Grass Pokémon. Mamoswine tries using Take Down on it twice, but it doesn't work. Dawn orders Mamoswine to concentrate all its power on one point, and in doing so Mamoswine is revealed to know Hidden Power. Mamoswine unleashes its new move, easily defeating Team Rocket.
The next morning, Ash has Grotle supply Tangrowth with an almost endless supply on energy thanks to its Synthesis. Though Brock points out that Grotle can only use Synthesis so many times. So, Mamoswine willingly lets Tangrowth use Absorb on it. Tangrowth rewards it with a Sitrus Berry and signals that it has enough energy to try to use Growth again. Verona finds a part of the tree still alive, and suggests they aim for it. So, once again, all the Grass Pokémon use Growth on the tree, and it is restored back to its original form. Tangrowth thanks Mamoswine, who now has its full confidence back.