This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Finfolk (Orkney)
In Orkney folklore, Finfolk (sometimes Finnfolk) are sorcerous shapeshifters of the sea, the dark mysterious race from Finfolkaheem who regularly make an amphibious journey from the depths of the Finfolk ocean home to the Orkney Islands. They wade, swim or sometimes row upon the Orkney shores in the spring and summer months, searching for human captives. The Finfolk (both Finman and Finwife) kidnap unsuspecting fishermen, or frolicking youth, near the shore and force them into lifelong servitude as a spouse.
The Finman is described as being tall and thin with a stern, gloomy face. He is said to have many magical powers, such as rowing between Norway and Orkney in seven oar-strokes, making his ship invisible and creating fleets of phantom boats. The Finwife starts her life as a beautiful mermaid bent on acquiring a human husband. Should she succeed, she takes him to live with her in Finfolkaheem, or, on occasion in some stories, goes to live with him instead.