This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Cirein Croin (Scottish)
Ceirean, Cirein-croin or cionarain-cro, was a large sea monster in Scottish Gaelic folklore. An old saying claims that it was so large that it fed on seven whales: Local folklores say this huge animal can disguise itself as a small silver fish when fishermen came in contact with it. Other accounts state the reason for the disguise was to attract its next meal; when the fisherman would catch it in its small silver fish form, once aboard it changed back to the monster and ate him.
This eating habit of his leads us to believe that Cirein-Cròon might be a malevolent creature. Since it is highly unlikely that eating humans would be a sustainable diet considering his size. Indeed, an old rhyme talking about the beast said that it could easily eat seven whales. This can mean that his habit of hunting humans might be more for sport.