1.
Extract the OBB contents:
- Rename the .obb file to .zip, e.g., main.123456789.com.example.game.obb becomes main.zip.
- Use a zip tool like 7-Zip, WinRAR, or the built-in unzip command in Linux/macOS to extract the archive. Note: OBBs are often stored without compression, store mode, so extract carefully to preserve file structure.
2. Locate and edit relevant files:
- Browse the extracted folder for the files you need to modify. In IL2CPP games, look for global-metadata.dat in assets/bin/Data/Managed/Metadata/. This file contains type info, strings, and offsets that must align with your edited libil2cpp.so.
- If your mod requires changes here, e.g., updating metadata to reflect code alterations in libil2cpp.so, use a hex editor like HxD or a specialized tool like Il2CppInspector/Il2CppDumper in reverse, though editing metadata is advanced and error-prone—small mismatches can crash the game.
- Rarely, some games place a copy of libil2cpp.so or other .so libraries inside the OBB, e.g., under lib/ or a custom path, for dynamic loading or anti-tamper reasons. If that's the case for your game, edit it the same way you did the APK's version—use your dumping process, dump.cs, to find offsets, then patch with a hex editor or ARM assembler.
- For other data files, e.g., JSON configs, asset bundles, edit them directly if your mod targets game values not in code.
3. Repack the OBB:
- Once edited, zip the folder back up. Use store mode, no compression, to match the original—e.g., in 7-Zip, set compression level to "Store"; or via command line: zip -r -0 new.zip extracted_folder/*.
- Rename the new .zip back to the original .obb filename, it must match exactly, including the version/patch number in the name, like main.123456789.com.example.game.obb.
- Ensure the file size and structure align closely with the original to avoid detection or loading issues.
4. Install and test:
- Uninstall the original game to avoid signature conflicts.
- Install your modified, signed APK.
- Manually place the modified OBB in the correct device path: /Android/obb/<package.name>/ e.g., /Android/obb/com.example.game/. You may need root or ADB for this if not using an emulator.
- Run the game. If it still fails, verify your patches with a debugger like IDA Pro or Ghidra on the running process, or check logs via ADB, adb logcat, for errors like metadata mismatches or integrity checks.
If your mods are simple, e.g., hex patches to existing functions without structural changes) you might not need to touch the OBB at all—double-check your offsets in dump.cs against the lib version, as they can shift between game updates. Some games also have runtime integrity checks on libil2cpp.so, which could silently disable mods; bypassing those often requires additional patches to anti-cheat functions in the lib itself. If the game uses custom encryption on OBB contents, you'll need to decrypt first, tools like Unity Asset Bundle Extractor can help for assets. Test on an emulator like LDPlayer or BlueStacks for easier iteration.
