Bug Report

How can the crash be reproduced?

Launch game with mod 1.16.4 jar file installed in 'mods folder' any version of Forge 1.16.4. I understand this is not a 1.16.3 crash report but it seems pertinent that this is reported and likely that the crash reporting template just hasn't been updated yet.

Crash Report and Logs

Originally I attempted to run it alongside a mod I'm developing to see how other mods interact with mine.
crash-2020-11-21_22.44.02-fml.txt

I think this error has to do with the way you have set up log-stripping.

Finding the mod to be, unfortunately, unfunctional, I created a clean instance of 1.16.4 in MultiMC (essentially software that allows multiple concurrent instances of Minecraft to be used and get their console information, essentially no different to the regular vanilla jar), installed Forge 35.1.0, placed BiomesOPlenty-1.16.4-13.0.0.420-universal.jar in the mods folder and ran the game. Instead of giving the above error, it just closes the game and exits with code -1. I believe this is an issue with reflection as, looking over your code, you seem to use methods of reflection that I am quite unfamiliar with. This method just doesn't seem to work though, as it produces this crash log:
crash-2020-11-21_23.01.43-client.txt

Mod Version

1.16.4-13.0.0.420

@Backjurns Delete your existing BOP config

i have had the same issue but on the regular Minecraft Launcher

crash.txt

@Forstride what do you mean by that im not in to this stuff! What do i need to do.

Delete everything in /.minecraft/config/biomesoplenty/

If you can't find that, look up a tutorial

now this is coming up
@Forstride

report.txt

this is the crash report

That doesn't seem like an issue with us. Try deleting all of your configs.

im sorry for the inconvience i have caused you and thank you becausee deleating all my configs worked!! :)

Just noticed you put out a new version of the mod as I was typing up the previous issue and it still has a very similar crash report:
crash-2020-11-21_23.07.44-client.txt

Could you please try using the regular Minecraft launcher, not MultiMC. We don’t use reflection anywhere in the mod, we use access transformers. This seems to imply to me that those access transformers aren’t being applied correctly which might potentially be a MultiMC issue

It looks like you're right. It launches on regular Minecraft. I'm relatively new to modding and am not sure why there are two different crash reasons for launching it alongside my mod in IntelliJ and launching it with MultiMC. Two different kinds of access transformer failures? If you do not feel this issue can reveal anything further, feel free to close it.