Timberjack

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 along with other dragons such as the Typhoomerang and each wing has at least 2 hooks, indicating that it has four "limbs" in total coming out of its 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."

Its body shape in total strongly resembles that of a Typhoomerang, but being 'leg-less'.

How To Train Your Dragon (film)
The Timberjack's only appearance in the film is in the Dragon Manual when Hiccup is attempting to research information on Night Furies. Like most dragons in the Dragon Manual, the Timberjack is considered "extremely dangerous" and should be "killed on sight".

In Book of Dragons
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. 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.

Trivia

 * The Timberjack is one of the bigger dragons like the Scauldron, Typhoomerang, Boneknapper, Whispering Death, Screaming Death and the Snaptrapper.
 * The Typhoomerang's body shape and design may have been based on a Timberjack, except with legs.
 * Given the above note (if it's true), the Timberjack might not appear in Wild Skies, as it would basically be the same as having another Typhoomerang, except with no legs.
 * The Timberjack's name is a combination of the words "timber" and "lumberjack".
 * In School of Dragons, there is a Timberjack named Stokehead. He is used only in the Hero Dragons Flying Corse through a forest. This means he must belong to someone, but to who is unknown. Another Timberjack is seen in School Of Dragons standing nearby a bridge with it's wings curled up around it. Besides the Timberjack in Book Of Dragons, and the upcoming Timberjacks in How To Train Your Dragon 2, these two game Timberjacks are some of the only ways we can see the Timberjack's attributes.
 * In the first How to Train your Dragon 2 trailer, a pair of Timberjacks are seen flying with Hiccup and Toothless. It's possible that one of them is Stokehead.
 * The Timberjack appears to be the symbol on the cover of the Book of Dragons.
 * The Timberjack likes to collect wood, which it uses to attack people and other dragons. It does this by secreting a few drops of oil based fire to burn them.
 * The Timberjack is actually one of the kinder dragons on Berk. This is evidenced by the fact that, on the ground, it likes to use its wings like a makeshift tent to shelter weary riders, keeping them warm and safe from the elements and other dragons.
 * The Timberjack is normally a very peaceful dragon, (this is the reason it leaves in peaceful forests), but can be dangerous if angered, betrayed, or offended.
 * When a Timberjack attacks, it is known to flail it's wings around, chopping anything in their path with the sharp edges of their wings.
 * Even though it's wingspan is huge, the Timberjack can slice through trees in its way without hindering its flight.
 * Judging from their name, attacks, and lifestyle, Timberjacks probably spend most, if not all of their life in dense, wooded forests. However, the Dragon Riders have flown through several forests and a Timberjack has never been shown. This could be because they don't live all the time in forests, that they are really secretive, or just don't live in the specific forests that the riders were flying through.
 * The Timberjack likes serenity, but can be very fierce when they are attacking something, or protecting their riders.
 * The Timberjack seems to have a stringy "beard" under it's snout. Since the traditional lumberjacks ends to have a beard, this makes the Timberjack's name even more similar to a lumberjack.
 * In the Timberjack's segment in Book Of Dragons, the Timberjack that sliced Bork has teeth facing downward, while all the other Timberjack's teeth face upward. This could be a difference between genders, a difference between ages, or just a mistake on the part of the animators.
 * Because the Timberjack has not been officially shown outside of Book Of Dragons yet, it is unknown if it uses it's ember-like fire to attack its enemies or defend it's friends, or if just uses its oil fire or it's sharp wings to do the same job.