If you want an old mod or modpack to run (Minecraft 1.2.4 and older), this is for you. Warning, not for newcomers!
- If you are on Android, install MiXplorer and MiX Archive
- Make a copy of the Minecraft version you want to modify
- Rename the custom version folder, .jar and .json to your desired custom version name (for example, foo, foo.jar, foo.json)
- Open the custom version's .json with MiX's Text Editor
- Remove
"downloads:{"client"...}
as shown in the screenshot
- Change
"id": "1.2.4"
to"id": "(your custom version name)"
- Change
"mainClass": "net.minecraft.launchwrapper.Launch"
to"mainClass": "net.minecraft.client.Minecraft"
- Save the .json
- Modify your .jar as desired, make sure to delete the
META-INF
folder afterwards. - Start up your custom version!
- If your game is stuck at the Mojang screen afterwards, try deleting options.txt
- This guide is NOT for Babric or Cursed Fabric!