Pokémon: Showdown at Dark City

In the middle of a terrible desert, our heroes inadvertently wandered into Dark City. With no name but Dark, the city has fallen into ruin. The streets, even at midday, are vacant of people. But suddenly, a rare figure appears and begins to throw stones at Ash and friends. They had heard at a restaurant in town, that this town contains two authorized Pokémon gyms, but that their Masters try to battle traveling Pokémon trainers anywhere within the town. This is said to be the cause of the town's desolation. Will our heroes also be caught up in the whirlwind of these battles?