Here's how it works:
1. Transfer Pokemon from HeartGold to Pokemon Ranger: You can use the "Mystery Gift" feature in HeartGold to receive a "Special Code" for Pokemon Ranger. This code allows you to transfer Pokemon to your copy of Pokemon Ranger.
2. Transfer Pokemon from Pokemon Ranger to Battle Revolution: You can then connect your Pokemon Ranger game to the "Nintendo Wi-Fi Connection" and upload your Pokemon to Battle Revolution.
Important Notes:
* This process only works for certain Pokemon and is limited to the Pokemon Ranger games.
* The Nintendo Wi-Fi Connection service is no longer active, so you cannot transfer Pokemon from Pokemon Ranger to Battle Revolution anymore.
Alternative Options:
* Pokemon Bank: You can use Pokemon Bank to transfer Pokemon from HeartGold to later games, such as Pokemon X/Y or Pokemon Omega Ruby/Alpha Sapphire. These games can then be connected to the Pokemon Global Link, which offers online battles similar to Battle Revolution.
* Home: You can use Pokemon Home to transfer Pokemon from other games to the cloud, which can then be accessed on compatible Nintendo Switch games. This allows for online battles and trading with other players.
While you can't directly transfer Pokemon from HeartGold to Battle Revolution, these alternatives offer similar functionality and provide a way to enjoy online battles with your favorite Pokemon.