The Modifier Code
Enter this Code into your Action Replay DSi to activate the HeartGold modifier cheat.
94000130 FCFF0000
62111880 00000000
B2111880 00000000
00000D14 01ED0001
D2000000 00000000
94000130 FDFF0000
62111880 00000000
B2111880 00000000
DA000000 00000D16
C0000000 00000027
D7000000 00025A68
D2000000 00000000
The National Pokedex
The National Pokedex is the in-game listing of every Pokemon in existence. In the Pokedex, every Pokemon has a number associated with it. To make the modifier work, you need to know the number of the Pokemon you want to acquire using the modifier. You can either look its number up online, or you can do it in-game by getting the National Pokedex. To get it, you need to defeat the Champion of the Pokemon League, then go visit Professor Oak in Olivine City.
How to Use the Modifier
Once in the game, hold down the "L" and "R" button on your DS. This will deposit 493 Master Balls into your inventory. Throw away the Master Balls until they equal the National Pokedex number of the Pokemon you want to find. Once you've done this, exit your inventory. Hold the "L" button down, and you'll enter a fight against your chosen Pokemon.
Mew
In Pokemon HeartGold, Mew is the singe most sought-after Pokemon. Its powers and stats are far above average, and because of the fact you cannot capture it without either cheating or using a complex glitch, Mew has acquired an almost legendary status among fans. However, if you use the Pokemon HeartGold Modifier to fight and capture Mew as a Wild Pokemon, it will never obey your commands.