Fun fact about single-biome worlds in 1.18: terrain shape is unaffected. For example here is a single-biome desert world. Everything is desert biome in this picture - the cliffs, the ocean, the mountain, etc. Biome is kind of like a layer of paint applied to the existing terrain. http://pbs.twimg.com/media/FDrSxTTXoAMBw5N.jpg