TheKodeToad

I don't think it's (ever) as simple as giving one of the devs a ring. Currently, Mojang only provides the log generated by their obfuscater of choice, ProGuard. This log...

Ah, well clearly there was a problem freezing the mapped registry. I think we're gonna need the full log. And the code around where the error actually happens. Show something...

If you are using Eclipse, adding "-Xverify:none" to the arguments may fix it. Only do this if you know that you will not be executing untrusted code.

"src/test" has nothing to do with server side code. If you want to run the server, you can use my fork, which merges jacobo's changes and updates to 1.18: https://github.com/TheKodeToad/MCP-Reborn

By the way, I haven't tested it. "src/test" is for testing your code. It is used by many projects to test whether the code is reliable. For example, you may...

I'm pretty sure that the location of patchy is https://libraries.minecraft.net/com/mojang/patchy/1.3.9/patchy-1.3.9.jar.

https://github.com/MinecraftForge/ForgeGradle

You need to do ./gradlew setup first. Backup everything in src/main/java in case it is erased.

OptiFine uses MCP, and it works alongside Forge mods. Forge and Fabric is theoretically possible, but it hasn't been achieved yet.

Likely for the Minecraft jar to be in ".minecraft/versions/VERSION_NAME/VERSION_NAME.jar". What launcher do you use?