Pokémon Brown

Originally released in the early 2000s, Pokémon Brown completely replaces Kanto with a brand new region (called Rijon), complete with its own story, trainers, gym leaders, Pokémon distribution and new elemental types.

Early versions only included the first 151 Pokémon, but later editions include a vastly expanded Pokédex (up to Generation IV, with a certain special Generation VI guest star) and other features such as an expanded type chart, additional dungeons and the ability to interact with Generation II games with a patch. You can even travel all the way to Johto!