The Timberjack is the name of a gigantic species of dragon. It appears to have a head that is of a similar shape to the Monstrous Nightmare and has a long slender neck, body, and tail. Its wingspan is huge such as the typhoomerang and each wing has at least 2 hooks, indicating that it has four "limbs" total coming out of it's sides. It is confirmed in the Dragon Training Academy game on the HTTYD website that it walks using these limbs to move around, like "legs."
The Timberjack's razor-like wings are its primary weapon, being sharp enough to cut down even the tallest trees in flight. Although it has not yet made a physical appearance, the dragon is said to be extremely dangerous.
In Book of Dragons, it is described in the manual as being one of the dragons in the Sharp Class, which are marked by vanity and a sharp weapon (in this case, the Timberjack's wings). This dragon attacks from out of the sky with its razor-sharp wings. It can slice through a forest of trees like a giant guillotine. It also has the ability to shoot hot, explosive embers. The Timberjack possesses no arms or legs, only its wings and long tail; but has been seen to stand up on its tail like a snake would. Unfortunately, its long wings make it impossible for the dragon to scratch its back. However, it has been discovered that if one scratches any hard-to-reach places for it, the Timberjack will be your friend forever.