Screenshot from the episode.
"The Tower of Terror" (Japanese: ポケモンタワーでゲットだぜ!; literally: "Capture at the Pokémon Tower!") is an episode of the animated TV series Pokémon: Indigo League which makes suitable viewing for Halloween. It first aired on TV Tokyo in Japan on September 2, 1997 and first aired in the United States on October 6, 1998.
Plot[]
On their way to Lavender Town, Ash and Co. arrive at Pokémon Tower. They hear screaming from the tower and are afraid to go in. They eventually go in, but leave the place because they are scared by a trick the ghosts played and leave Ash and his Pokémon to explore the place alone. They meet a Haunter and Gengar trying to be funny, but Ash does not find it amusing. Just as they are about to leave, Ash crashes after them causing a light fixture above to fall on him and Pikachu, knocking them out. Haunter pulls their spirits out of their bodies and plays with them for a while to make them realize how lonely they are. Ash says he cannot stay for long because he must become a Pokémon Master. Just as Ash gives up on catching a Ghost-type, Haunter goes with him and scares Misty and Brock.