Mud

Mud is a block found abundantly in mangrove swamps, or created by using a water bottle on a dirt block.

Breaking
Mud can be broken by hand, but using a shovel speeds up the process.

Natural generation
Mud generates in the mangrove swamp biome.

Post-generation
Mud can be obtained by a water bottle on dirt, coarse dirt, and rooted dirt, transforming it into a mud block.

Usage
Mud is not a full block, and as such, it has some unique properties; entities standing on mud sink slightly into it, similar to soul sand. Unlike soul sand, however, mud does not slow the movement speed of mobs or players that walk on it. Falling blocks such as sand also drop as an item when landing on it, and a hopper that is under a mud block can collect items dropped on top of it.

In Bedrock edition, mud behaves as a full block. Entities do not sink into it, and hoppers placed beneath mud cannot collect items dropped on top of it.

Most blocks that can be placed on full blocks can still be placed on mud.

Clay
If mud is placed directly above a block that has pointed dripstone underneath, it eventually turns into clay. This makes clay renewable.