Disclaimer

This project is for educational and archival purposes.

Gen 3 Shiny Odds CLI Patcher

It's a small script I made a while ago as practice. Works with European and USA versions only, haven't checked JP at all, feel free to fork and add it!

Safe shiny-odds patcher for Pokemon Gen 3 GBA ROMs:

• FireRed
• LeafGreen
• Ruby
• Sapphire
• Emerald

Safety model

• CRC32 ROM auto-detection (only known clean revisions are accepted)
• Strict byte validation at every patch offset before writing
• Never overwrites the input ROM (always writes a new output file)

If CRC32 is unknown, patching is refused.

Usage

python shiny_patcher.py "Pokemon Emerald.gba" --odds 4096

Guided mode (recommended for beginners):

python shiny_patcher.py --guided

If no input_rom is provided, guided mode starts automatically:

python shiny_patcher.py

Arguments:

• input_rom: source .gba ROM path
• --odds N: desired shiny rate as 1 in N (required)
• --output PATH: optional output ROM path
• --overwrite-output: allow replacing an existing output file
• --guided: interactive wizard, scans a folder for ROMs and guides patching
• --folder PATH: folder to scan in guided mode (default: current directory)

Default output naming:

• <input_stem>.shiny_1inN.gba

Example:

python shiny_patcher.py "Pokemon FireRed.gba" --odds 2048 --output "FireRed_1in2048.gba"

Guided scan of a specific folder:

python shiny_patcher.py --guided --folder "C:\ROMs\GBA"

Notes on odds conversion

Gen 3 uses a threshold internally (base threshold is 8, equivalent to 1/8192). This tool converts 1 in N to the nearest threshold with:

• threshold = round(65536 / N)
• clamped to 1..255 (ROM instruction encoding limit at target offsets)

Supported ROM CRC32 values

• 0xF0815EE7 - Pokemon Ruby Version (USA, Europe) Rev 0
• 0x61641576 - Pokemon Ruby Version (USA, Europe) Rev 1
• 0x554DEDC4 - Pokemon Sapphire Version (USA, Europe) Rev 0
• 0xBAFEDAE5 - Pokemon Sapphire Version (Europe) Rev 1
• 0xDD88761C - Pokemon FireRed Version (USA) Rev 0
• 0x84EE4776 - Pokemon FireRed Version (USA, Europe) Rev 1
• 0xD69C96CC - Pokemon LeafGreen Version (USA) Rev 0
• 0xDAFFECEC - Pokemon LeafGreen Version (USA, Europe) Rev 1
• 0x1F1C08FB - Pokemon Emerald Version (USA, Europe) Rev 0

Verify syntax quickly

python --version
python shiny_patcher.py --help

<<<<<<< HEAD

Drag-and-drop launcher (Windows)

Use patch_drag_drop.bat for simple usage:

• Drag one or more .gba ROM files onto patch_drag_drop.bat
• The launcher reads odds from patcher_config.ini
• It calls shiny_patcher.py and creates patched ROM output files

Edit this line in patcher_config.ini to change odds:

odds=4096

Example values:

• odds=8192 (vanilla)
• odds=4096
• odds=2048 =======

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License

Distributed under the MIT License. See LICENSE for more information.