Gaetbeols/mudflat shore biomes

In rare parts of the world, most notably in the west coast of South Korea, you can find a gaetbeol, a massive mudflat that is revealed and submerged in depending on the tides. It is home to many small sea creatures like fish, crabs, and shellfish. In Minecraft, this biome would have 1 layer of soft mud that regenerates like water. Sea creatures such as nautilus would spawn and run around inside the mud and you can scoop them up with a bucket when you shovel the mud and expose the creature for a brief moment. The soft mud would be semi-transparent, even more than a slime block, making it a bit easier to search for these mobs. Soft mud can also be dehydrated into mud the same way you turn mud into clay.