Wolf-Fangs are medium-sized dragons mentioned in How to Betray a Dragon's Hero.
Wolf-fangs are described as being monkey-like in that they jump and climb from tree to tree, yet they are also wolf-like. They do have wings, but rarely use them.
Wolf-fangs have night vision that is depicted similar to the view from night vision goggles, as seen below:
In The Incomplete Book of Dragons, Wolf-fangs are said to have excellent hearing, smell, in addition to X-ray vision.
Wolf-fangs are pack-hunters, and they kill without mercy. Cressida Cowell notes that they are untrainable.
During the Dragon Rebellion, Wolf-fangs remained unaligned.
Wolf-fangs are discussed in this reference book in the chapter on Tree dragons, as well as appearing in the 'Dragon Key' at the back of the book.
A pack of Wolf-fangs appear at the beginning of Book 11. They are running along a river, having spied a human in distress in it.