My superflat world is almost entirely covered in Dreadlands biome simply because I summoned Cha'garoth, The Dreadbeast. Is there anyway to stop him from slowly devouring my world and converting it into his own land?

I don't know how to make a question on this site so I decided to make it into an issue article.

Your best bet would be to not spawn him, and if spawned, kill him. Cha'garoth is the only thing unaffected by any config option in place to stop the plague spreading.