Full grown Steam Wyvern from the Halloween mystery egg batch for:

More eggs in the Halloween batch are still for sale over here: https://www.furaffinity.net/view/21347721/

Steam Wyverns are steam powered machines given life by a captured soul. Some know how to create more of their kind, but the capturing and introduction of a soul is a difficult process, often requiring the help of someone or something else with more abilities. They require only water as sustenance which is boiled to provide them with power. Excess steam expels from between their armor plates and mouths. It is unknown how the first was made, but it is thought that someone performed a soul binding ritual on a machine they created.

Information on Steam Wyverns here: http://www.furaffinity.net/view/20822976/
Adoptable size chart can be found here: https://www.furaffinity.net/view/21326887/