I'm using RpgDifficulty as a server-side mod and it seems to work just fine with vanilla clients. The only downside is that you can't see the nameplates so I was wondering if you could make it so it works with vanilla clients by renaming the mobs on the server side. Maybe toggling an option so the mods stops sending packets to the vanilla client.
Thanks.

edit: maybe you could do something like this mod https://modrinth.com/mod/healthcare
(compatibility with it would be awesome)

Closing as the dev's goal is not to provide one-sided mods

Source: developer's discord server