BoneKnapper

The Boneknapper is a species of dragon thought to be almost mythical by Vikings due to it's rare nature. As it's name may suggest, the Boneknapper spends it's time scouring the land for pieces of bone in order to create the perfect armor. Sometimes, this bone armour 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 it's nature as well, as with most dragons around Berk.

Appearance
They are large creatures with one pair of wings and one pair of legs. They are bi-pedal and walk like a nadder. Without their bone armour, they are rather, flimsy with very soft hide. Some bones are essential for a BoneKnapper, allowing it to do simple abilities like roaring! They can spend a lifetime searching for the perfect bone for their hide.

Tamed BoneKnappers may start using man-made objects as part of their armour, like cartwheels and pieces of metal, if not too heavy.

Abilities
They breathe a very powerful fire breath, and a roar piercing enough to crush bones (or so they say).

Strengths and Flaws
Their hide makes them weak, so they create a bone armour to defend themselves

Habitat
Animal graveyards, places where you can find bones frequently.

Preferred Training Methods
If you help them out with their armour, they will be forever grateful.