From the Rumblehorn species, Skullcrusher is part of a previously undiscovered class -- tracker class, being that he's the bloodhound of dragons.

He can find anything on scent, like when he found Hiccup in Valka's nest based only on Hiccup's lost helmet. Skullcrusher looks like a truffle pig mixed with a rhino, but much bigger. He has the chitinous green-red iridescent coloring and surfacing of a scarab beetle and keeps his battle axe-shaped muzzle in the dirt, sniffing things out.