Pokémon : S3 | E5 – Illusion Confusion!

While on their way to Violet City, Ash and his friends get lost in the middle of a deep forest. While the others complain about the situation, Ash tells them to follow him, saying their troubles will be over in no time. Despite his optimism, the group is still unable to get out of the forest and Misty becomes increasingly frustrated. As the night settles in, eerie sounds echo from the trees, which appear to gain menacing faces. Frightened by this, the trio runs to another part of the forest. Once again, however, they are confronted with the same trees every way they turn. As they flee, a Hoothoot appears and uses Foresight, returning everything to normal.

Bewildered, the trio stops to catch their breath. Suddenly, Gary emerges from the trees and tells them that everything they saw and heard was an illusion and commends Hoothoot on a job well done. After scanning Hoothoot with his Pokédex, Ash is mocked by Gary for being unprepared. Gary advises his rival to get a Hoothoot if he wishes to make it out of the forest. Confused, Misty asks Gary why he is still in the forest if he has a Hoothoot. Gary tells her that he has been busy catching Pokémon and lost track of the time. After Gary departs, Ash and his friends search for a Hoothoot, but their efforts are in vain.
(Source: Bulbapedia)