This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Muldjewangk (Australian Aboriginal mythology)
The Muldjewangk is a water-creature in Ngarrindjeri mythology that inhabited the Murray River, particularly Lake Alexandrina. It was used as a deterrent for Aboriginal children who wished to play near the riverside after dark. Sometimes they are portrayed as evil merfolk, and other times as a gargantuan monster. Accounts are inconsistent as to whether there are many of the creatures, or a single "The Muldjewangk".
A legend tells of a Muldjewangk who once attacked a steamboat owned by European settlers. The captain saw two great hands grasping the hull of the boat so he grabbed his gun. Aboriginal elders on board warned the captain not to shoot, but their pleas fell on deaf ears. The elders warned the captain that he would suffer as a result of his actions. Soon after, the captain broke out in weeping red blisters over his body, and took six months to die.