This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Ichchhadhari Nag (Hindu)
A common male cobra will become an ichchadhari naag (male shape-shifting cobra) and a common female cobra will become an ichchadhari naagin (female shape-shifting cobra) after 100 years of tapasya (penance). After being blessed by Lord Shiva, they attain a human form of their own, have the ability to shape-shift into any living creature and could live for more than a hundred years without getting old.
Ichchadhari naags and naagins possess the gem called naagmani, considered much more valuable than any precious stone, it has revive power. Legends tell of many people dying through snake bites when they try to steal the naagmani. When a naag or a naagin is killed, the image of their killer will be imprinted in their eyes. The partner or family of that naag/naagin will identify the killers by this image and take revenge.