"A Festival Trade! A Fesival Farewell?" is an episode of the animated TV series Pokémon XY: Kalos Quest which makes suitable viewing for Halloween. It first aired in the United States on September 26, 2015.
Plot
Ash, his friends, and Team Rocket have just arrived at a costume festival to have a good time. During the festivities, Jessie sees a Pumpkaboo falling in love with hers. She decides to do something to help it, but things go the other way around.
Later in the episode, Pumpkaboo evolves into Gourgeist. This is the first time in the Pokémon Anime that Gourgeist appears.
See the article on XY082: A Festival Trade! A Festival Farewell? on Fandom's Pokemon wiki.