Ash's Muk (Japanese: サトシのベトベトン Satoshi's Betbeton) was the ninth Pokémon caught by Ash during his travels through Kanto.
Ash caught Muk in the episode Sparks Fly for Magnemite. Ash and his friends were traveling through Gringey City, which was in the midst of a power failure. The local power plant was being overrun by the mysterious Poison-type Pokémon, Grimer. After the swarm was located, the Grimer's leader, a Muk, came and challenged the Trainers. However, the vast numbers of Magnemite and Magneton in the city combined attacks to clear out the Grimer, leaving only Muk. With the aid of Pikachu and a Magnemite that was following it due to an electrical build up, Ash defeated and captured the Muk. It was then immediately sent to Oak's lab because its stench was so rancid that it could seep through the Poké Ball. However, Muk's horrid smell seemed to have disappeared in later episodes as neither Ash, nor anyone around him, was affected by it.
Muk's first battle was in The Fourth Round Rumble, where it was selected for use in the Indigo Plateau Conference. After Jeanette Fisher's high-level Bellsprout had trounced Bulbasaur and Pikachu, Muk made a surprise appearance as Ash's third Pokémon. Muk easily absorbed Bellsprout's physical moves and Razor Leaf and then simply smothered Bellsprout with Body Slam, winning the match for Ash.
Muk was briefly called in The Mystery Menace, where Ash used Muk to help him and Tracey find Misty,Togepi, and Bulbasaur, who was kidnapped by a giant Bulbasaur in a sewer. Muk and Kingler also offered to fight for Ash in the Orange Island Championship battle against Drake in Hello, Pummelo!, but Ash chose Tauros instead.
Muk was reunited with Ash when he returned home in A Tent Situation. Muk insisted on fighting Team Rocket, and Ash ordered it into battle instead of choosing Bulbasaur. Muk managed to resist Razor Leaf attacks from James's Victreebel, and showed off its newly learned Poison Gas when it bit down on it in an attempt to use Poison Powder. Lickitung's Lick was even less effective, wiping Muk's face ineffectively to the point of causing pleasure instead of damage. It was then put to sleep by Sleep Powder, but awoke after Gary intervened and drove Team Rocket away.
Muk's only other major battle was when Ash called it up from Oak's Lab in Can't Beat the Heat!, along with Heracross, Tauros andSnorlax in order to fight Gary in the Silver Conference. It was sent out originally to fight Blastoise, and the two fought to a stalemate, with Muk's Sludge Bomb deflected by Rapid Spin and Blastoise's physical attacks absorbed into Muk's body. Ash pulled Muk for his Bayleef quickly after. It was sent out to fight Scizor later, who dodged a Sludge Bomb easily. Whilst Muk absorbed both Quick Attack and Metal Claw, Scizor was able to throw Muk, and defeated it with Swift.
Muk made an appearance in the special episodes, where it was seen crushing Cassidy, Butch and all of the stolen Poké Balls. It was also seen crushing Tracey when he opened the door to Oak's Lab to Delia.
Advanced Generation series
Muk appeared in The Right Place and the Right Mime when Ash returned to Pallet Town. It greeted Professor Birch with its usual friendliness.
Diamond & Pearl series
Muk reappeared in An Old Family Blend!, at Professor Oak's lab, and then it was transferred to Ash for a brief reunion. Muk was not seen participating in the Lily of the Valley Conference.
Best Wishes series
Muk has made brief appearances in New Places... Familiar Faces! and Farewell, Unova! Setting Sail for New Adventures!, smothering Professor Oak while Ash was calling him from Professor Juniper's laboratory.
Muk was reunited with Ash in The Dream Continues!, where it and the rest of Ash's Pokémon posed in a group photo with him.
Personality and characteristics
Ash's Muk is an extremely happy and affectionate Pokémon. It grew an attachment in particular to Professor Oak and as a recurring gag, it would always smother the Professor whenever Ash would make a call to the lab. This was first seen twenty episodes after its capture, in Who Gets To Keep Togepi?. Muk tackled Professor Oak in excitement in Showdown at the Po-ké Corral, when Oak explained that Muk and Krabby had become just like him from its long period of living with him.
Muk's affection also extends to his Trainer, second in enthusiasm only to Bayleef, despite only having fought for him on three occasions. Muk obligingly crushes Ash in excitement whenever Ash returns to the lab or summons it to his party. Its affection also extends to complete strangers, as was seen when it completely ignored Jessie's Lickitung in order to hug her, also smothering James's Victreebel in excitement. It also smothered Professor Birch upon meeting him in The Right Place and the Right Mime.
Its affection even extends to antagonists, as seen both in the aforementioned encounter with Jessie and James, and also in a special episode, Showdown at the Oak Corral, when it actually appeared sad thatTotodile drove Butch and Cassidy away. As Professor Oak said to Jessie, Muk loves humans, and it is not very particular to which kind.
Muk differs from most of Ash's other Pokémon in that it is a defensive Pokémon, with a low attack power and very few moves used across its entire time on the show. It has never been shown to be damaged by a physical attack, with its opponents' moves always absorbed by its odd body type. Despite being quite powerful and good in battle, it has only ever defeated one opponent, Bellsprout (it was put to sleep by Victreebel and knocked out against Gary without a win).