Pokémon (1997)

S1E74 The Ancient Puzzle of Pokémopolis

During their training session, Ash and his friends stumble upon the remnants of Pokémopolis, an old city shrouded in mystery. As they dig deeper into its history, they witness a colossal Gengar and a massive Alakazam gearing up for a showdown. Just when the tension escalates, a giant Jigglypuff shows up and uses its lullaby to send both Pokémon into a deep slumber.