Johto is the second Pokémon region. It is the first to introduce new Pokémon since the series' first released. The Johto region consists of the discovery of 2 Pokémon types, Steel-Type and Dark-Type, as well as a few other discoveries such as those that consist of different evolutions, such as Pikachu being evolved from Pichu and the like.
The region was also to be discovered to sit right next to the Kanto region. Because of that, both regions share the same Pokémon League. So far, these 2 regions are the only ones to have done this as other regions went on to have their own Pokémon Leagues.
Johto anthem: The Johto Journeys Theme - Long version (Pokémon)
Ikran's OoT/Pokémon crossover[]
It's been mentioned that Zelda II had caught a variety of Pokémon and brought them over to Hyrule. Chikortia was actually her first Starter Pokémon and she's actually born from Goldenrod City.
The ReBoot Multiverse[]
It's been mentioned that Akari had caught a variety of Pokémon during her first journeys, and her Starter was her Meganium named Freya; she was actually born and raised in Goldenrod City.
Recessional of the Red Dragons[]
April was born there and was the reigning Pokémon Champion following her cousins' budding legacy. She and her team helped the special forces win the interstellar war against the Red Dragon Syndicate.