The game runs slow. Solution: HeartGold is heavy on DS hardware. Use MelonDS instead of Desmume for better frame rates. Also, disable "Audio Sync" in emulator settings.
To get started, most players use the Universal Pokemon Randomizer. This tool doesn't provide the ROM itself but acts as a modifier for a clean file you already own. You simply load your HeartGold ROM into the program and begin toggling the settings that suit your playstyle. pokemon heartgold randomizer rom
Technical setup is straightforward but requires specific tools. You will need a DS emulator like DeSmuME or MelonDS if playing on a PC, or a flashcart if you prefer original hardware. Once you run your ROM through the randomizer tool, it generates a new, unique file. It is vital to save your "seed" string; this code allows you to share your exact randomized world with friends so you can race through the same chaotic version of Johto together. The game runs slow