a sponge server I play on will not load an existing world, with your mod installed.
https://pastebin.com/FffKEUjs

I've managed to get some changes in to Forge to provide me with a way to implement this mod without the need for the core mod.
Once SpongeForge supports a version of Forge in which this technique is available I will take another look at this. Hopefully compatibility with Sponge can be achieved now I no longer rely on class transformation.

Thanks for the report, I'll investigate.

If it helps at all, I installed your mod to our server and couldn't start the server with your mod and sponge installed.

spongeforge-1.10.2-2477-5.2.0-BETA-2637
bettermobgriefinggamerule-1.10.2-4.0.1

fml-server-latest.log

It didn't crash the server, just prevented it from starting.

After further investigation I found that the coremod part of this mod is causing the issues with Sponge, as it is trying to transform the same class.
Unfortunately there is no easy fix since Sponge replaces all mobGriefing checks with its own implementation. It does however mean that it might be relatively straight forward for me to convert this to a Sponge plugin in the future, but at the moment I don't know how that will work since I have no experience with Sponge.

I'll keep this issue open until I have looked in to the feasibility of writing this as Sponge plugin and decided whether to tackle it or not.