From Bulbapedia, the community-driven Pokémon encyclopedia.
The Mareep Festival is a small annual festival, held in a small ranching valley in Johto. The competition is a beauty pageant for Mareep, as well as a battle tournament for Mareep alone. Only Trainers who live in the area are allowed to enter the festival.
The Mareep Festival was depicted in the anime episode Mild 'n Wooly.