: Because it is a scene dump of the base game, it contains all the original mechanics of HeartGold , including the Johto and Kanto regions, following Pokémon, and the Pokéathlon.
: A popular fan game (not a ROM hack) featuring an entirely new region (Eldiw) and a "Xenoverse" dimension with unique Pokémon forms.
If you are writing a guide or "paper" on this topic, here is a suggested outline:
Using its psychic power, Uxie releases a subtle, memetic wave across Johto and Kanto. It doesn't erase memories; it poisons them. Citizens begin to distrust anyone with a Pokémon not native to their specific town. Soon, the fear escalates to hatred. Johto descends into a fragmented, paranoid region where every gym leader refuses to battle trainers with "foreign" teams.