Rumblehorn

"This dragon is more than strong. It's fast, it's smart and it's elusive."

- Hiccup

The Rumblehorn is a medium-sized Tracker Class dragon that first appeared in How to Train Your Dragon 2.

Official Description
"A Rumblehorn's nose knows! From the Tracker Class, it can follow the faintest scent anywhere. There is nowhere to hide from this Dragon! When a Rumblehorn doesn't want to move, it doesn't move... but when a Rumblehorn makes a charge, opponents clear out of the way!"

- Dragons: Rise of Berk

Development
The Rumblehorn was inspired by a rhinoceros, a truffle pig, a dung beetle, a jackhammer, and a battle axe.

Early concept art depicted the Rumblehorn with a triple split jaw, much like the Catastrophic Quaken and Snaptrapper. This was one of Character Designer Nico Marlet's signature designs.

Egg
Rumblehorn eggs appear to have a slit that runs down vertically and separates the two halves of the egg. They have a few small indents on its base.

Hatchling to Adult
The Rumblehorn has relatively large wings, a wide torso, and a tail with a club-like hammer on the tip. Its most notable feature is the heavily armed front half of its body with firm armor plates on the neck and a large lower jaw, a battle axe-shaped muzzle, which is always digging in the dirt, looking for scents, and two, very sharp, elongated horns resembling those of ceratopsian dinosaurs, but lacking a beak. The Rumblehorn has a very acute sense of smell and is determined to track down and find anything once it has picked up the scent. In total, they look like a mix of truffle pig, a rhinoceros, a battle axe, and a scarab beetle.

Titan Wing
Titan Rumblehorns appear to have developed a shiny green armor. There are more plates to their armor and it appears harder. The horns on their head are sharper and longer, and their wings are cyan in color. Furthermore, their tail has grown more spikey tips.

Firepower
Rumblehorns can shoot long-ranged fire "missiles" from their mouths that initially starts out as a white-hot fireball that quickly solidifies and turns to a warmer color before it ends up in a sooty, stony material when it hits its target.

Senses
As members of the Tracker Class, the Rumblehorn's powerful sense of smell allows them to find any Viking's scent from long distances, even if the material has been in the water for a long time. They can find anything based on scent alone.

According to DreamWorks Dragons: To Berk and Beyond!, the only thing Rumblehorns cannot smell is dragonberries.

Strength and Combat
Rumblehorns are extremely strong dragons, for they are able to carry large Vikings and their weapons, as well as ramming down a sea stack and a warship while flying at full speed.

Judging by their body shape, it is quite possible for these dragons to charge at their opponents and impale them on their horns and to use their powerful tail as a club.

Intelligence
Rumblehorns appear to be extremely intelligent, hiding from their enemies in bushes and creating traps with their footprints. They have also been shown to attempt to chase Hiccup and the gang off Dragon's Edge by pretending to harm them and other native dragons and destroying buildings. They have even outsmarted Hiccup and the gang numerous times.

Speed and Agility
For their body size, Rumblehorns are known to have surprising speed and agility on land, and they use this to charge like rhinoceroses. As for flight, they are able to spin in the air with no difficulties at all. Their tails are flexible enough to swing all the way around to their heads.

Disaster Detecting
As shown by Skullcrusher, Rumblehorns are able to detect any disasters that will happen a few weeks early, as Skullcrusher was able to sense an oncoming tsunami before any other human or dragon on the island.

Stealth and Camouflage
Despite their large size, Rumblehorns are able to move silently. Their heavy body is able to hide in bushes in order to camouflage with their green scales.

According to Eret in To Berk and Beyond!, Rumblehorns will fire a blast in the air then promptly fly through it. This will temporarily burn off their own scent and make them impossible for another dragon to track.

Endurance and Stamina
As shown by Skullcrusher, Rumblehorns are able to take a shot from a Singetail and fall from a high altitude to the ground and still get back up easily. They also have a large amount of stamina, as Rumblehorns have shown the ability to run at high speeds to charge at their enemies and fly farther distances than many other dragons.

Communication with Other Dragons
Rumblehorns are able to scare other dragons into the air by either roaring or pounding the ground with their heads.

Weaknesses
According to Eret in To Berk and Beyond!, Rumblehorns cannot smell Dragonberry juice. Applying to oneself will mask the scent and make the person untrackable by a Rumblehorn.

Behavior and Personality
"Rumblehorns may have tough hides, but they still require a gentle touch."

- Valka

Rumblehorns always have their snouts to the ground, sniffing around for something edible. They can be aggressive, but they are friendly towards their riders. Their food of choice is unknown, but it is known that they are carnivorous. They are also highly intelligent and determined. They run like rhinoceroses. As shown by the still wild Skullcrusher, Rumblehorns can be very caring and protective of those who are in danger, as seen when Skullcrusher tried to warn everyone of a tidal wave heading towards Dragon's Edge. Rumblehorns appear to be solitary and elusive creatures that are rarely seen due to their keen sense of smell.

Season 1
Hiccup and the gang face a strange new dragon that has been targeting native dragons during the events of "Crushing It", and it destroying Dragon's Edge. Hiccup named it the Rumblehorn. They get Gobber to build a fortress, but to no avail. Eventually, Hiccup allows his father to help them get rid of the rouge Rumblehorn but it always outsmarts them. Back at the Edge, it attempted to attack Gobber and Toothless was told to shoot him down. Sensing that something was not right, Stoick tamed the Rumblehorn and brought the gang to the sea. Hiccup then realized that a large wave strong enough to destroy the Edge was heading their way and the Rumblehorn was trying to chase them away from the island in order to save them. Eventually, they worked together to surround the island with Gobber's fortress and the Rumblehorn, together with Stoick, collapsed a sea stack just in time to stop the wave. Stoick then keeps the Rumblehorn as Thornado's replacement and calls him Skullcrusher.

Season 5
In a flashback shown in "The Wings of War, Part 1", Stoick saw Drago Bludvist and Krogan riding Rumblehorns after burning down the hall where the gathering took place.

Dragons: Rise of Berk
The Rumblehorn, along with its Titan form and the individuals Skullcrusher and Seedling Rumblehorn, a subject of the Foreverwing, were made available in this game.

School of Dragons
The Rumblehorn in this game has an exclusive chest available too.

Trivia

 * The Rumblehorn shares a similar body structure with the Triceratops, with both having horns on their heads and a thick neck armor.
 * Its lower jaw seems to have been originally a split jaw, as evidenced of a piece of concept art.
 * The Seedling Rumblehorn slightly resembles a tortoise.