Complex sentence: Hoppip's main anime appearance was in the episode "Foul Weather Friends", in which, Ash and Friends meet a Hoppip trainer called Mariah, who used Hoppip to predict the Weather.
Split into simpler sentences: Hoppip's main anime appearance was in the episode "Foul Weather Friends". In it, Ash and Friends meet a Hoppip trainer called Mariah, who uses Hoppip to predict the Weather.