Changing the flat worlds is so easy by customizing the layers. For instance, the game allows you to create diamond worlds or water worlds. You can make use of this mod to design a particular terrain or set up a new map.
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How to Play Custom Flat Worlds Mod?
After opening BlockLauncher, you can design a new Minecraft world. There is a variety of layers to text the name of the world. Check the IDs of these blocks here.
Choose Flat world because the game works only with flat terrain.
Then, create the world by choosing “Play.” The layers are available in the world. Depending on your favorite blocks, you can have a suitable combination.