This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Svartalfar (Norse)
In Norse cosmology, Svartalfar, also called myrkalfar are beings who dwell in Svartalfheim, "home of the black-elves". Both the svartalfar and Svartalfaheimr are primarily attested in the Prose Edda, written in the 13th century by Snorri Sturluson.
Scholars have noted that the svartalfar appear to be synonymous with the dwarfs and potentially also the dokkalfar ("dark elves"). As dwarfs, the home of the svartalfar could possibly be another description for Nioavellir ("dark fields").