Mud

Mud is a decorative block obtained 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, and it can also be obtained by a water bottle on dirt, coarse dirt, and rooted dirt, transforming it into a mud block.

Usage
Entities standing on mud sink 2 pixels into it, similarly to soul sand. Unlike soul sand, however, mud does not slow the movement speed of mobs or players that walk on it.

Mud, not being a full block, has some unique properties; falling blocks such as sand drop as an item when landing on it, a hopper that is under a mud block can collect items dropped on 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.