java.lang.IllegalArgumentException: No such class exists: IRegistryCustomDimension

We will need more information about this. This only happens inside that specific dungeon and I was unable to reproduce it in another one.

What do you need to be able to play it?

I can't access the dungeon thats the problem and since its a paid asset I cant ask you to send parts of it too, I want you to binary search your functions and using this method pinpoint the faulty function for me and send that part of the config here. I know its a bit of tough work but its the only way for me to reliably reproduce and fix the issue.

By binary search I mean, deleting half of the functions in the functions.yml of that dungeon, seeing if the error is still there, if it is, then you know the faulty function is in the other half. Keep repeating this to pin point the faulty function.

Before you start though make sure the issue is related to a function, delete the functions.yml file completely (make a backup of it first of course) then see if the issue is gone, if it is let me know here, if not follow the instructions above.