How to obtain Koraidon in Johto

Obtaining Koraidon

To obtain Koraidon, you must first complete the Pokémon League and unlock time travel to the past with Celebi. Go to Tohjo Falls with Celebi in the first slot and use one of the compatible characters: James, Jessie, female Rocket or male Rocket in Kanto, or male Rainbow or female Rainbow in Alola. You can change the character under Menu > Options > Player.

If you have already completed this part of the story, interact with the radio to return to the past. Once there, go to the Ruins of Alph with Celebi and five past Paradox Pokémon in your party. You must be in the past for Koraidon to appear.