This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Niohoggr (Norse)
In Norse mythology, Niohoggr is a dragon who gnaws at a root of the world tree, Yggdrasil. In historical Viking society, nío was a term for a social stigma, implying the loss of honor and the status of a villain. Thus, its name might refer to its role as a horrific monster in its action of chewing the corpses of the inhabitants of Nastrond: those guilty of murder, adultery, and oath-breaking.
The only person capable of controlling him is the goddess Hel. Its existence is the portend of the Ragnarok that signals the end of all where he will escape as his body is "dripping with corpses" while flying low across the blazing plains. He is usually depicted as a all-black dragon with huge wings. Sometimes, he has the appearance of a dark grey dragon with a pair of horns similar to tree's branches with a pair of white eyes.