Pokémon : S5 | E31 – Some Like It Hot

Ash and his friends make their way through some rugged terrain, still bound for Blackthorn City. Misty complains about the increasing heat. Brock points out that there are volcanoes and hot springs around, which doesn't please Misty at all. Meanwhile, Team Rocket is relaxing in the hot springs when Meowth spots the group walking past. However, Jessie and James return to their relaxation, declaring that the twerps are the reason for their stresses. A huge geyser suddenly erupts beneath the Rocket trio, sending them blasting off.

Later, Ash and Misty get into a passive-aggressive argument because of the heat. When a Magcargo appears, Ash checks his Pokédex for information on it. Brock notices more Magcargo around them. Misty remains irritated and urges her friends along, and eventually, the group finds a cooler place. They continue through a narrow mountain pass until they come across a sleeping Magcargo blocking the road. Ash yells at it to move out of the way. As a result, Magcargo wakes up in a foul mood and aims a Flamethrower at them. The group manages to duck in time to avoid the flames, and Magcargo returns to its nap. Ash decides to battle it, but Misty tells him that she'll handle it instead because a Fire type like Magcargo is weak against Water types. She is about to send out Staryu when her Psyduck comes out instead. Psyduck approaches Magcargo and wakes it up. Psyduck is intimidated by Macgargo's rage and rushes behind Misty's legs for safety. Misty is annoyed and calls out her Poliwhirl to douse Magcargo with a Water Gun. Magcargo immediately withdraws into its shell to avoid the water. When it emerges, it retaliates with a Rock Slide. Poliwhirl evades the attacks Magcargo throws at it, but it fails to avoid the Flamethrower attack and is knocked out by it, forcing Misty to recall it.
(Source: Bulbapedia)