Pokémon : S3 | E1 – Don’t Touch That ‘dile

Ash and his friends are walking through a foggy forest for New Bark Town in order to register for the Johto League. Ash notices a familiar tree branch and declares that they must be lost. Misty scolds Ash, and the two of them get into an argument, which Brock is forced to break up. Togepi senses something and promptly hops out of Misty's arms, prompting the others to follow. The group is startled after seeing a mysterious blue Pokémon on a formation in the middle of a small pond. When the Pokémon notices them, it runs away. Ash tries to follow it but falls off a steep edge, and Pikachu and Togepi soon follow. Becoming alarmed by his disappearance, Misty and Brock go after Ash, but they also trip and fall. Jigglypuff walks by and seems to find it fun before sliding down the hill as well.

Meanwhile, Team Rocket is also lost in the same fog-filled forest. They become hungry and decide to run, and soon find themselves out of the forest and staring at a large building. The trio is started by a horde of Fearow and rushes inside what is actually a Pokémon Lab. A voice suddenly speaks up, and the group soon finds the source, Professor Elm. He is too busy looking through his microscope to realize the visitors are Team Rocket; thinking it is Nurse Joy, he tells them to check up on his Totodile. They encounter Totodile shortly after, and it bites onto Meowth's tail and sprays a Water Gun at James's face. Posing as Nurse Joy, Jessie says she will bring Totodile back to the Pokémon Center before picking Totodile up and running out of the lab, followed by James and Meowth.
(Source: Bulbapedia)