Byteandahalf, developer of the WIP redstone mod, has another new mod- this one lets you customise the layers in a superflat world! Usually you’d have to edit a special file in the app to change this, but 12bit’s mod lets you enter the layers when creating a world.
To enter your layers, simply start with a [, followed by a block ID, and ended with another ].
To add multiple layers, simply add more IDs separated commas, as shown in the screenshot. That will generate a world with a bottom layer of bedrock (as that is the last ID), then a second layer of sandstone, bedrock, then grass on top.
Get it at the link below! It’s for Android AND iOS, so everyone can enjoy it.