This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Ichneumon (Medieval Bestiaries)
In medieval literature, the ichneumon or echinemon was the enemy of the dragon. When it sees a dragon, the ichneumon covers itself with mud, and closing its nostrils with its tail, attacks and kills the dragon. The ichneumon was also considered by some to be the enemy of the crocodile and the asp, and attack them in the same way.
The name was used for the pharaoh's rat, mongoose, or Egyptian mongoose (Herpestes ichneumon), which attacks snakes; it can also mean otter. It is believed that many dragon deaths over the years were caused by Ichneumons. The Ichneumons are notoriously known for not simply just being the cause of dragon deaths, but for their willingness to fight to the death with one.