You need a legal backup of the Pokemon HeartGold (USA or Europe version) ROM file. This is usually in a .nds format. Step 2: Download the Universal Pokemon Randomizer

I sent out THE ECHO. The screen turned pitch black. A single line of text scrolled across the bottom, slower than the game’s usual speed: THE ECHO used REMEMBER.

Save the new file and load it into your favourite emulator (like DeSmuME or MelonDS).

To start, you need a standard NDS (Nintendo DS) ROM file of Pokémon HeartGold. Look for a file with the extension.

Encounter a Mewtwo on Route 29 instead of a Sentret.

A Pokémon HeartGold Randomizer is a modified version of the original 2009 game where specific elements are completely shuffled using a software tool. Instead of playing through the standard script, a randomizer alters the game's internal data. You can customize exactly what gets shuffled, including:

There is a specific, almost sacred moment in every Pokémon HeartGold player’s life: you step onto Route 29, Poké Balls shaking in your digital satchel, and instead of a meek Sentret or a stubborn Pidgey, a wild Kyogre stares you down. Your level-5 Chikorita trembles. You laugh. You panic. And just like that, you are no longer a trainer—you are a survivor.

If you’re tired of seeing the same Pidgeys on Route 29, it’s time to spice things up. A Pokémon HeartGold Randomizer