Effects on walking
When the player walks on mud, they will slow down to 50% of their normal speed. After getting off of it, they will turn the next three blocks they walk on (if they are Grass Blocks) into Dirt, as if they were tracking Mud onto the Grass.
When smelted, Mud will turn into Dirt. This will also occur if it is left in a Desert, Savanna or Mesa Biome for 2 or more Minecraft days.