This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Namazu (Japanese)
In Japanese mythology, the Namazu is a giant underground catfish who causes earthquakes. The creature lives under the islands of Japan and is guarded by the god Takemikazuchi enshrined at Kashima, who restrains the catfish with a stone. When the Kashima-god lets his guard fall, Namazu thrashes about, causing violent earthquakes.
Widespread connections between catfish and earthquakes in Japan were not present until the late 17th century, and only rose to popularity as symbolically causing or predicting earthquakes during the 19th century. The association of the namazu with earthquake seems to have first occurred in the area around Lake Biwa, around the 16th century.