This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Knucker (English)
Knucker is a dialect word for a sort of water dragon, living in knuckerholes in Sussex, England. "The word comes from the Old English nicor which means "water monster" and is used in the poem Beowulf. It may also be related to the word "Nixie", which is a form of water spirit.
The Knucker is said to have wings, and is sometimes described as a sea serpent. The Knucker has "a giant, slithering sea serpent's body, and cold, bold sea serpent's eyes and a deadly, hissing sea serpent's mouth". It was believed that knuckers could be found at knuckerholes in various places in Sussex, including Lyminster, Lancing, Shoreham and Worthing.