Pathless Plain is a Mirage Spot located east of Pacifidlog Town and south of Route 131. However, Pathless Plain will only appear if you have at least three Pokémon with maximum EVs in your team.
The Mirage Spot has a portal on the northwest side where you can battle Cobalion, Terrakion, or Virizion, depending on the day of the week.
Soaring Location
Wild Pokémon
Interactable (Portal)
