The Mud Kingdom is the home and territory of the MudWings. It forms the back of Pyrrhia which is right under the Sky Kingdom's wing and next to the Rainforest Kingdom and the Kingdom of the Sea. Queen Moorhen currently rules the Mud Kingdom. There is also a delta and a ravine/fissure mentioned in The Dragonet Prophecy, where a battle took place between Blaze's army and the MudWings.
The Mud Kingdom is a vast marshy swampland with clusters of mud structures made by MudWings. Turtle describes it as dreary, swampy, and bog-riddled. The kingdom is mostly various forms of wetland, with rivers, including the Diamond Spray River, which feeds into the Diamond Spray Delta in the north. Diamond Spray Delta is where the lowest born MudWings are born, according to Kestrel. The kingdom also contains areas of grassland with a few trees here and there, with some of the grasslands hypothetically being used for agriculture. All over the kingdom, there are MudWings hiding or sleeping in the mud.
Where the Mud Kingdom meets the Kingdom of the Sea, the forest and ocean are separated by a strip of sandy beach. Where it meets the Rainforest Kingdom, there is an area of swampy, foggy forest that gradually transitions into the rainforest.
Queen Moorhen's palace is the MudWing tribe's palace, where the queen and her siblings reside. It is located next to a large lake at the southern edge of the Mud Kingdom, about a day's flight from the rainforest. It is composed of gloppy, endless swamps, and emits an incessant sound of gurgling water.
The Diamond Spray Delta is known for being the home of the lowest-born MudWings. It was first mentioned by Kestrel in The Dragonet Prophecy. There is a path of dried dirt that runs through the delta's village. On either side, there are large mud puddles for MudWings to sleep and hunt in, as well as sleep houses. Sleephouses are tall mud towers that each MudWing troop sleeps in. Generally, one troop sleeps in a certain sleep house.
The Diamond Spray River is a river that leads down from the Sky Kingdom to the Diamond Spray Delta.
The Dragonet Prophecy
Clay, with Glory, met his mother, Cattail, along with his siblings Reed, Pheasant, Umber, Marsh, and Sora near the Diamond Spray Delta, which — according to Kestrel — is where "the lowest-born MudWings crawl." The dragons of the Mud Kingdom lived with their sibling units in huts made of mud with holes in them to enter and exit.
The dragonets and Webs walked along the outskirts of the Mud Kingdom to get to the rainforest. Starflight claimed Queen Moorhen's palace is near a large lake and only a day's flight away. They also found two dead MudWing soldiers who were killed by the NightWings.
Sunny and Clay went to the Mud Kingdom so they could use their dreamvisitor to visit the dreams of the MudWings to try to get a message to Burn about the meeting outside of her stronghold. They learned that the MudWings were planning an assault on the IceWings, and managed to convince Queen Moorhen to drop the idea.
The Jade Mountain Prophecy
Umber briefly recalled memories of him and his siblings when they were together in the Mud Kingdom.
Chameleon briefly mentioned that the Mud Kingdom is tolerable.
Turtle passed the Mud Kingdom on his way to find Anemone.
The Lost Continent Prophecy
While studying in the library, Clearsight considered running away to the Mud Kingdom.
Throughout the book, Wren thought about the kingdom and its geography.
In order to break the MudWings' alliance with Blister. Deathbringer wrote a note mentioning that the coast of the Mud Kingdom would never be the SeaWings' land. Commander Piranha threatened General Swamp that they will actually take the land if the MudWings insisted that they were innocent.