critical

Two mods clash inside this pack

Q: What does "MixinApplyError: Mixin [create.mixins.json:LevelRendererMixin] from phase [DEFAULT] in config [create.mixins.json] FAILED during APPLY" mean?

Two mods clash inside this pack. A mod patched the game expecting a library or another mod that is missing or the wrong version, so the game crashed when that code ran. The stack trace names the mod (look for handler$...$modname, or the .mixins.json config). Remove or exclude that mod server-side, update it to a build for this exact version, or ask the pack author to ship its missing dependency.

Q: How do I fix "MixinApplyError: Mixin [create.mixins.json:LevelRendererMixin] from phase [DEFAULT] in config [create.mixins.json] FAILED during APPLY"?

1. Read the mixins.json name: In "Mixin [create.mixins.json:LevelRendererMixin] ... FAILED during APPLY", the mod is Create. The config name is nearly always the mod id. 2. Check that mod against the game version: Open its CurseForge or Modrinth page and look at the version list. A mod built for 1.20.1 will fail exactly like this on 1.20.4, and the download page shows which builds match. 3. Look for a second mod on the same class: If the mod is the right version, another mod is patching the same method first. The class name in the error narrows it: an OptiFine, Sodium or Iris mixin failing on a renderer class usually means two rendering mods, and one has to go. 4. Remove or update, then restart: Update the mod to a build for your exact game and loader version, or remove it. If this is a pack, exclude it server-side and tell the pack author which mixin failed; they will want the line. 5. Check the dependency line above: Sometimes the mixin fails because the mod needs a library that is missing. The loader logs the missing dependency first, above this error, and installing it fixes both.

What it looks like in your log

MixinApplyError: Mixin [create.mixins.json:LevelRendererMixin] from phase [DEFAULT] in config [create.mixins.json] FAILED during APPLY

What causes it

A mod patched the game expecting a library or another mod that is missing or the wrong version, so the game crashed when that code ran.

How to fix it

The stack trace names the mod (look for handler$...$modname, or the .mixins.json config). Remove or exclude that mod server-side, update it to a build for this exact version, or ask the pack author to ship its missing dependency.

Why it happens

A mixin is how a mod patches the game: it injects code into a Minecraft class at load time. The injection describes the exact method and the exact spot it expects to find. If that method is not there, because the game version is different or another mod already rewrote it, the injection fails and the whole class fails to load. The server dies during start-up or the first time that class is touched.

The error names the mixin config, which is a file inside one mod, and the class it was patching. The mod that owns the config is the one at fault, whatever the stack trace below it looks like. The stack trace is the game trying to load a class that was never patched properly; it is a symptom.

Fix it step by step

1Read the mixins.json nameIn "Mixin [create.mixins.json:LevelRendererMixin] ... FAILED during APPLY", the mod is Create. The config name is nearly always the mod id.
2Check that mod against the game versionOpen its CurseForge or Modrinth page and look at the version list. A mod built for 1.20.1 will fail exactly like this on 1.20.4, and the download page shows which builds match.
3Look for a second mod on the same classIf the mod is the right version, another mod is patching the same method first. The class name in the error narrows it: an OptiFine, Sodium or Iris mixin failing on a renderer class usually means two rendering mods, and one has to go.
4Remove or update, then restartUpdate the mod to a build for your exact game and loader version, or remove it. If this is a pack, exclude it server-side and tell the pack author which mixin failed; they will want the line.
5Check the dependency line aboveSometimes the mixin fails because the mod needs a library that is missing. The loader logs the missing dependency first, above this error, and installing it fixes both.

If that didn't work

AbstractMethodError with no MixinApplyError is the same family with a different presentation: a mod is calling a method that the current version of another mod no longer has. The first mod class in the stack trace is the caller; update it.

"Reference map could not be read" lines nearby are noise, not evidence. They only matter when a real injection failure follows them.

Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.

Check your own log