Each tradition has its own set of mystical creatures. Dragon's are regarded as a national symbol in China. Grippen ( eagle face, lion body) in the middle east, Phoenix ( the bird which rises from ashes) of Greece, sphinx ( human face, lion body) in Egypt, etc.
India is the oldest civilization, we have the highest number of mystical creatures recorded in our history books. We have given special emphasis to snakes. We find a reference to snake King Takshak and the Shesha Naga on which Lord Vishnu resides. Finally, there was a snake called Kalia on whose head Lord Krishna danced.
One of the interesting mythological creatures is called Icchadhari Nag and Nagin. Icchadhari means one who can achieve anything and nag means cobra. With its "will power", the Ichhadhari snake can assume any form, like a human or any other animal. It is said, the snake which has not used its poisonous glands, accumulate the poison and convert it into the crystal called "Nag Mani". This Nagmani has great powers and one who posses it becomes the master of those powers. These creatures take vengeance if you hurt them. Its claimed, numerous people who tried to steal the Nag Mani thereby causing hurt to the snake were bitten to death by the snake. These snakes can recognize people.
Now we will come from mythical to reality. King cobra, is the only snake in the world, who has the brain big enough to identify a person. Olden days the treasures would be buried under the ground. While digging them, you would find snakes, as the snake lives in burrows underground. So the snakes were associated with treasures.
Snakes life is very difficult, and for it not to use poison ( evil intentions) for a hundred years requires very strong will power. Any person with such will power, even in difficulty becomes Icchadhari, which means he/ she can achieve anything in life.
Were these mythical creatures a way to give moral to the next generations?
Irrespective of this, "These mythical creature exists, at least in the minds of people who believe in them."