What if GF tried to make several pokemon have subtle physical changes depending on the region? These changes can still be visible when traded to another game as well. They can be as subtle as gender differences, while also adding variety to older pokemon.

For example, Kanto and Johto-born Pikachu can have paler stomachs, longer tails, or chubbier proportions to reflect its original design. When traded to a Sinnoh, Kalos or Unova game, this Pikachu will still have these differences.