This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Si-Te-Cah (Paiute)
According to reports of Northern Paiute oral history, the Si-Te-Cah, Saiduka or Sai'i were a legendary tribe who the Northern Paiutes fought a war with and eventually wiped out or drove away from the area, with the final battle having taken place at what is now known as Lovelock Cave near Lovelock, Nevada, United States. They had red hair, and are often (though not always) described as having been cannibals.
In some versions of the legend they were giants. In 1911, a large amount of artifacts and mummified human remains were discovered under three to six feet of guano by guano miners in Lovelock Cave. "Si-Te-Cah" means "tule-eaters" in the Northern Paiute language. Tule or Schoenoplectus acutus is a fibrous water plant. In order to escape harassment from the Paiutes, the Si-Te-Cahs were said to have lived on rafts made of tule on Lake Humboldt.