This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Sirin (Slavic)
Sirin is a mythological creature of Rus' legends, with the head of a beautiful woman and the body of a bird (usually an owl), borrowed from the siren of the Greek mythology. According to myth, the Sirin lived in Iriy or around the Euphrates River.
The legend of Sirin might have been introduced to Rus' by Persian merchants in the 8th-9th century. In the cities of Chersonesos and Kyiv she is often found on pottery, golden pendants, even on the borders of Gospel books of tenth-twelfth centuries.