The dragons known by the Hairy Hooligan Tribe are grouped into one of seven classes based on their characteristics and abilities. The seven classes are Stoker, Boulder, Fear, Sharp, Tidal, Mystery, and Strike. In the exclusive short, Book of Dragons, the idea to categorize dragons into individual classes was started by Gobber's great-great-great grandfather named Bork the Bold.
Dragons in this class have very little known about them. In this class are the Changewing, the Boneknapper, and the Smothering Smokebreath. Also, according to the How to Train your Dragon Live Spectacular's program book, the Red Death is a mystery class Dragon.
- The Grapple Grounder is not grouped in any of the classes mentioned above, nor does it have one of its own. Though it's been described as being rather similar in behavior to a Night Fury, as well as having very similar firepower, it could be a Strike Class dragon.
- Since the vikings didn't know what a Night Fury looked like until the taming of Toothless, the Strike Class should logically be symbolised by the Skrill. It is possible that the Strike class's symbol was changed by the Hooligans to have a new symbol after the taming of Toothless.