InvalidMixinException: Mod Mixin Failed to Apply

What the log looks like

org\.spongepowered\.asm\.mixin\.transformer\.throwables\.InvalidMixinException
/\*\s+Invalid Mixin\s+\*/

How to fix it

1. Open your latest.log or crash report and look for 'Mixin apply for mod' or the 'Config :' line inside the 'Invalid Mixin' banner to identify the exact mod that failed.
2. Check the culprit mod's download page and verify the jar file matches your exact Minecraft version (for example, a 1.21.4 mod will often fail with this error on 1.21.5).
3. Update both the offending mod and your mod loader (Fabric, Quilt, Forge, or NeoForge) to their newest releases, or downgrade the mod by one version if the crash started right after updating it.
4. If the error mentions a rendering or world class (such as EntityRenderer or Chunk), test without heavy bytecode-modifying mods like OptiFine, Sodium, or Sinytra Connector to rule out a class conflict.
5. Temporarily remove the identified mod so your game can launch, then send the full log to that mod author's issue tracker.

Check your own log