This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Melusine (Medieval folklore)
Melusine or Melusina is a figure of European folklore, a female spirit of fresh water in a holy well or river. She is usually depicted as a woman who is a serpent or fish from the waist down sometimes with two tails, as a serpent from the waist down, or as a dragon.
Melusine, a daughter of a human father and a fairy mother, could be said to have started life as a hybrid and in the course of her mythical career exhibited a number of different hybrid forms. Having transgressed against her father, she was cursed by her mother, the fairy Presine, to turn into a serpent every Saturday.