The Boneknapper is the titular main antagonist of the short film How to Train Your Dragon: Legend of the Boneknapper. It was thought to be almost mythical by Vikings due to its rare nature. As its name may suggest, the Boneknapper spends its time scouring the land for pieces of bones in order to create the perfect armor. Sometimes, this bone armor can be essential for the dragon to perform basic actions, such as roaring.
The Boneknapper will often go to extreme lengths to find the bones it seeks, hunting down the fragments for years. However, the dragon does has a docile side to its nature as well, as with most dragons around Berk.
The Boneknapper makes a brief appearance in the How To Train Your Dragon film. After Dragon Training, Hiccup reads through the Dragon Manual in order to find information on Night Furies and ends up finding a page about the Boneknapper as he flicks through the book. The Boneknapper appeared as the main antagonist in The Legend of the Boneknapper Dragon, a 15-minute short created for the release of How To Train Your Dragon on DVD. Originally having hunted down Gobber The Belch since his teen days numerous times, the dragon made its first physical appearance on a distant island after Gobber, along with Hiccup and his friends, set out to capture it. Hiccup realizes that Gobber's belt buckle is the piece of bone that the Boneknapper wants, which is missing from its neck. Reluctantly, Gobber gives the piece of bone back to the dragon, where it suddenly becomes quite docile and playful. As a reward, the Boneknapper lets Gobber, Hiccup and the others ride on its back to get home.
It is possible that the Boneknapper's closest relative is the Armorwing, because they have similar body structure. The only difference is that Armorwings use metals instead of bones to cover its body.