The dragons known by the Hairy Hooligan Tribe are grouped into one of seven classes based on their characteristics and abilities. The seven known classes are Stoker, Boulder, Fear, Sharp, Tidal, Mystery, and Strike. In the exclusive short, Book of Dragons and in episode 20 of Riders of Berk, the idea to categorize dragons into individual classes was started by Gobber's great-great-great grandfather named Bork the Bold.
Stoker Class dragons are hotheaded fire breathers, and most of them are capable of setting themselves on fire. They include the Terrible Terror, the Monstrous Nightmare, the Typhoomerang, and the Fireworm (whose queen can re-ignite other dragons' fires).
The known dragons in the Stoker class are Hookfang, Torch, Fanghook, the Monstrous Nightmare that Astrid trained, and the six Terrors trained by the teens (the only four of which named are Sharpshot, Iggy, Butt and Head).
Boulder Class dragons are tough and associated with the earth. They can eat rocks, and despite that their wings are smaller compared to their entire body, they are able to fly as fast and as high as most other dragons can. The Gronckle, Whispering Death, and the Screaming Death are members of this class.
Fear Class dragons are stealthy, sneaky, and often have multiple heads. Instead of fire, they breathe gases with different effects. The known dragons of this class are the Hideous Zippleback and the Snaptrapper.
The only known dragons in the Fear class is a Zippleback, the names Barf and Belch given to each separate head.
Tidal Class dragons live in and near the ocean, and unlike most dragons, they don't have fire breaths as their ranged attacks. These dragons are generally bigger in size than most of other classes, consisting of species classified in the large Dragons. The Scauldron, the Thunderdrum, the Oceanzap, and the Bewilderbeast are classed here.
Mystery Class dragons have 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 Night Fury used to be Mystery Class, but thanks to Hiccup, information on the Night Fury is now available.
The only known dragon in mystery class is the Boneknapper that Gobber befriended and the Red Death.
Strike Class dragons are most powerful, super fast, have pin-point accuracy, highly intelligent and have incredible vice-like jaw strength. They are also the most difficult to train, but the most loyal once trained. The dragons of this class are the Skrill and the Night Fury.
Unknown class is a temporally class for dragons that don't have a class. These dragons may possibly be sorted into different classes in the future. The current members are the Grapple Grounder, the Flightmare, and few other HTTYD 2 dragons.
- 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.
- It is possible that the Mystery Class is a sort of "temporary" class where dragons are put when little is known about them, and then when they are more thoroughly understood they are moved to another class. For instance, the Night Fury could have been a Mystery Class dragon before the events of the first movie, and then moved to the Strike Class once it was studied and trained by Hiccup.
- These seven classifications may not be the only ones in the future.
- At four known species,the Stoker class is the largest class, but the Tidal Class rivals this with four named species, but only two of those have currently been introduced.