When Jason and the Argonauts set out on a quest given to them by King Pelias to acquire the Golden Fleece, they had to first defeat the deadly Colchian Dragon. It is described as a giant serpent with three tongues and a long crest going down its back. Like Kerberos, it too was the offspring of Echidna and Typhon.
They are without a doubt Deadly in their purpose. They are as deadly as any protector I have come across. Once given a task, they will do all it takes, including serious bodily harm to get it done. they are single minded in their determination and will not rule out any means to get it done. Please be aware of this before you task them with anything. They are a dangerous breed and perhaps too much for a beginner but only you can decide that.
