During development, Psyduck was considered as the mascot of the other game instead of Eevee. This idea was scrapped because of Psyduck having similar colours to Pikachu.

The names of the post-game master trainers appear to be references to other outside media:
•The Pikachu master trainer Lass Iuke is a reference to voice actress Ikue Otani who voices Pikachu in the Pokemon anime.
•The Eevee master trainer Lass Aoi is a reference to Aoi Yūki, the voice actress for Eevee in the game.
•The master trainers for Zubat and Golbat, Scientist West and Scientist Keaton, are references to actors Adam West and Michael Keaton, respectively, who both played the superhero Batman.
•The master bird trainers Bird Keeper Barney, Bird Keeper Seymour, and Bird Keeper Moe, are possible references to the characters Seymour Skinner, Barney Gumble and Moe Szyslak from the animated series The Simpsons.
•The three ghost master trainers: Psychic Arin, Psychic Danny and Psychic Ross, are references to the members of the video game web series Game Grumps; Arin Hanson, Danny Avidan and Ross O'Donovan.