hgss-shiny-modifier

A Python script designed to change the Shiny Pokémon encounter rate in the Pokémon HeartGold/SoulSilver Nintendo DS games. Works by modifying the Shiny rate offset in the game ROM file. Now with automatic game version detection!

Features:

• Change the Shiny encounter rate to any desired value within the allowed range.
• Automatically detects the game version based on the game ID and selects the correct Shiny rate offset.
• Can be manually adjusted for different game versions and regions.
• Easy-to-use command line interface.
• Currently tested with North American HG/SS versions.

Dependencies:

Requires Python3 and the ndspy Python library. Install ndspy with pip:

pip install ndspy

Usage:

1. Place your .nds file (the game ROM) in the same folder as the shiny_rate_editor.py script.
2. The script will auto-detect the game version and use the correct Shiny rate offset. If you want to manually set the Shiny rate offset or the new Shiny rate, you can provide them as command-line arguments.
3. Run the script from your terminal, replacing <filename> with the name of your .nds file, <shiny_offset> with the hexadecimal value of your desired shiny rate offset (if you want to set it manually), and <new_shiny_rate> with your preferred shiny encounter rate. The shiny encounter rate should be a hexadecimal value between 0x0 and 0xFF.

# Arguments in [square brackets] are optional
python shiny_rate_editor.py <filename> [<shiny_offset>] [<new_shiny_rate>]

For example, if you have a file named pokemon.nds and you want to set the Shiny encounter rate to 0xFF (1/256, the maximum), you would use:

python shiny_rate_editor.py pokemon.nds 0x70080 0xFF

If you don't provide a shiny offset or new shiny rate, the script will use the default values based on the auto-detected game version and a default shiny rate of 0xFF.

4. The script will create a new modified game ROM file called shiny_rate_patched.nds. Use your method of choice to play the edited game ROM file.

Shiny Encounter Rate Offsets:

Here are the offsets for different versions of the game:

Language	Shiny chance
Japanese	0x6FAC0
Spanish HG	0x70078
Korean HG	0x7017C
Korean SS	0x70174
Others (Including North America)	0x70080

The script works by using ndspy to extract and decompress the raw ARM9 binary file from the game ROM. It then modifies the value used to determine Shiny encounter rates and reinserts the modified ARM9 binary back into the ROM file. Ideally, we would recompress the ARM9 binary before reinsertion, but this can cause crashes in some cases. So, we leave the binary decompressed, which seems to work just fine.

License:

This project is licensed under the terms of the MIT license.