This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Surma (Finnish)
Surma often accompanies the goddess Kalma, who is the daughter of Tuoni. He is the embodiment of violent deaths, and appears in several different forms, such as an axed man or an hellish hound (like the Greco-Roman Cerberus). Surma is a creature that guards the gates of the Underworld or Tuonela to prevent escape.
An often-used Finnish metaphor is surman suuhun "into Surma's mouth", as if the victim was mauled to death by Surma. A terrible beast, embodies sudden, violent death and guards the gates of the Underworld or Tuonela to prevent escape. It is often described as being a large dog with a snake-tail and can turn you into stone (with a stare).