Dark City is an anime-exclusive location that appeared in Showdown at Dark City.
Dark City was home to two rival Gyms that were unsanctioned by the Indigo Pokémon League: the Yas Gym and the Kaz Gym. Each hoped to become an official Gym by driving the other out of town, and would hire wandering Pokémon Trainers to fight for them. These battles came to resemble street fights more than anything else, and caused such damage to the town that Trainers earned a bad name amongst the inhabitants. The fighting grew even more intense as a Nurse Joy, who worked as an official League Inspector, was about to arrive in town to determine whether either Gym was worthy of becoming official.
Ash Ketchum and his friends arrived in Dark City shortly after the Kaz Gym Leader hired Jessie and James of Team Rocket to serve as bodyguards. After defeating them-an unremarkable feat for Ash and his friends-they were approached by the Yas Gym Leader about joining the Yas Gym, but refused. Realizing that the two Gyms were bent on destroying each other regardless of what harm or damage they might do, Ash's group and the townspeople caught in the middle of the struggle joined forces to stop the two gyms. Their plan revolved around a shared quality of the Yas Gym Leader's Scyther and the Kaz Gym Leader's Electabuzz.
The plan worked to perfection, with Scyther and Electabuzz being tricked into attacking their trainers and then each other. Nurse Joy then revealed herself and informed the leaders of both Gyms that neither would become an official Gym unless they could learn to treat Pokémon with respect, which she advised them to learn from Ash. The members of each Gym were soon put to work repairing the town.