This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Cu Sith (Scottish)
The cu-sìth(e) is a mythical hound found in Irish folklore and Scottish folklore. In Irish folklore it is spelled cu sídhe, and it also bears some resemblance to the Welsh Cwn Annwn. The cu-sìth is thought to make its home in the clefts of rocks and to roam the moors of the Highlands. It is usually described as having a shaggy, dark green coat and being as large as a small cow.
According to legend, the creature was capable of hunting silently, but would occasionally let out three terrifying barks, and only three, that could be heard for miles by those listening for it, even far out at sea. Those who hear the barking of the Cù-Sìth must reach safety by the third bark or be overcome with terror to the point of death.