This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Selkie (Faroese, Icelandic, Irish, and Scottish)
Selkies are mythological creatures that can shapeshift between seal and human forms by removing or putting on their seal skin. They feature prominently in the oral traditions and mythology of various cultures, especially those of Celtic and Norse origin. The term “selkie” derives from the Scots word for “seal”, and is also spelled as silkies, sylkies, or selchies.
Selkies are sometimes referred to as selkie folk. Selkies are mainly associated with the Northern Isles of Scotland, where they are said to live as seals in the sea but shed their skin to become human on land. Selkies have a dual nature: they can be friendly and helpful to humans, but they can also be dangerous and vengeful.