Mormo is a shapeshifting female entity who's known for having three forms: The first form, is a mocking vampire-like maiden who may or may not be wearing Victorian Era style clothing; Second, a gorgon-like creature with tentacles for hair instead of snakes; And lastly, a large toad-like creature with tentacles for a face, akin to her servitors the Moon-beasts.
|“||O friend and companion of night, thou who rejoicest in the baying of dogs (here a hideous howl bust forth) and spilt blood (here nameless sounds vied with morbid shriekings) who wanderest in the midst of shades among the tombs, (here a whistling sigh occurred) who longest for blood and bringest terror to mortals, (short, sharp cries from myriad throats) Gorgo, (repeated as response) Mormo, (repeated with ecstasy) thousand-faced moon, (sighs and flute notes) look favourably on our sacrifices!
|~ H.P. Lovecraft, "The Horror at Red Hook"|
In the Trail of Cthulhu RPG, Kenneth Hite says Mormo is Diana, Mab, Lamia, Lilith, Medusa, The Moon, and/or several other Gods, Titans, and Great Old Ones. He links her to vampires, werewolves, and dogs, and says she's an enemy of Bast. As with all of Hite's write-ups of Gods and Titans in that book, the Keeper (GM) is encouraged to decide which of the contradictory elements are true and which are mere myth or misunderstanding.
In Ancient Greek mythology, Gorgo and Mormo, along with Stheno, are given as names for the Gorgons, of whose form the originally very beautiful Medusa is given the likeness as a curse.