Thunderdrum

The Thunderdrum appeared in 2011 short movie called Book of Dragons. The Thunderdrum is a large Tidal Class dragon that was first mentioned in How to Train Your Dragon and first appeared in Book of Dragons.

Instead of breathing fire, the Thunderdrum produces a strong, concussive sound that can kill a human at close range. The blast is so powerful that the dragon is said to "get its power from Thor himself". Legend also has it that when the Thunderdrum hatches from its egg, it makes a sound so loud it rattles the sky. When not swelling its body up to yell, Thunderdrums can actually flatten their body by expelling all oxygen from their massive lungs for a limited period of time. In this sleeker state, Thunderdrums can better skim the ocean surface or even dive beneath the waves in search of prey. While it's true that Thunderdrums create tremendous amounts of noise, they also possess the ability to cancel out each other's sonic blasts. By modulating its roars to the proper frequency, a Thunderdrum can use its soundwaves to negate an attacking Thunderdrum's bellow, rendering it into a rather calming wave of white noise.

This dragon relies mostly on its two sets of wings, one primary and one smaller set to the rear, using them to get around and move through the water like a tornado.

These dragons have stubby legs and long, skinny tails. It also has a series of backward facing spikes sticking out of its back. The Thunderdrum's body resembles several marine creatures such as a basking shark, a whale shark, a manta ray, or a baleen whale. According to the Dragon Manual, Thunderdrums have really powerful wings and the spikes on their tails are very sharp.

In Dragons: Riders of Berk, this dragon is just bigger than a Gronckle (excluding the tail), but in How to Train Your Dragon 2, it is much bigger.

All Thunderdrums seen in adaptations before How to Train Your Dragon 2 are not much larger than medium or large-sized dragons. Baby Thunderdrums grow up to 11 inches tall.

In How to Train Your Dragon 2, much larger Thunderdrums are seen. These Thunderdrums are longer than Blue Whales and their wingspan is long enough for Toothless to fly under one that was jumping out of the water. The maximum size for these dragons is unknown. Thunderdrums in this size are probably too expensive to animate, so they are smaller in the Series.

They form pods in a hunt or on migration, a feature similar to those of cetaceans. Generally reclusive in nature when alone, living in sea caves and dark tide pools or in open waters.

Understandably, they are strident and assertive, the loud Thunderdrum always makes its feelings known.

Adolescents are shown to be mischievous to Vikings and dragons alike as they can be very annoying to them. Since they don't stop roaring or mimicking other sounds. However, the adolescents will acquiesce to any adult of the same species, regardless of relationship or lack thereof.

Thunderdrums are so stubborn that they can be tough to train. Thunderdrums show a real parental instinct to any young, even if it's not their own.

According to Hiccup in Race to the Edge, Thunderdrums have a habit of holding grudges against their enemies.

Powers and Abilities
Like nearly all dragons in the Manual, they are classified "extremely dangerous, kill on sight." Thunderdrums are experts in producing sound and have many of unique abilities related to sound waves.
 * Babies: It is also said that when a Thunderdrum hatches from its egg, it makes a sound so loud it rattles the sky. Baby Thunderdrums have the strength to be able to drag two young Vikings on its tail with no sign of struggle. As hatchlings, their thunderous roar is powerful enough to send heavy Vikings to the air and can destroy some large objects such as Hiccup's invention, the Thunder Ear.
 * Sonic Blast & Fire Blast: The name comes from its main mode of attack/defense. The Thunderdrum produces a strong concussive sound that can kill a human at close range. It is not only capable of temporarily stunning other dragons but also can even extinguish flames shot by other dragons. The blast is so powerful that the creature is said to "get its power from Thor himself." Only the Screaming Death has a tolerance with this attack (able to stun it temporarily). By combining roars of several individuals, the roars are able to knock away several large dragons at mid-distance. Like its sound wave booms, a Thunderdrum can shoot blue blasts of fire that get bigger the farther they go. And these fire blasts also travel at the speed of sound. The downside to this power is that it takes a lot out of a Thunderdrum to employ it, so it's not often used. Thunderdrums can blast waves of blue fire if necessary, but this uses a lot of energy. In order to protect themselves from their own sound emissions, the Thunderdrums developed a system to offset sonic blasts by regulating wave frequencies of blasts to neutralize others' roars.
 * Strength & Combat: Thunderdrums are some of the most powerful dragons. Thunderdrums are also some of the all-around most useful dragons as they can dive down to the depths of the ocean and fly at extremely high altitudes. Thunderdrums have been seen defeating wild dragons, pull two ships at the time with the added weight of Stoick the Vast, defeating a whole herd of wild boars and a wild specimen has been seen destroying a row of sea stacks by flying through them.
 * Endurance & Stamina: Their endurance and stamina are very impressive as shown by Thornado, who was able to take attacks from Stoick and still fly in great speed. Despite Hiccup referring to Stoick as a '400 lb man', the latter is only 350 lbs.
 * Agility & Prehensile Tail: They also have been shown to be quite flexible, as Thornado managed to grab Stoick with his prehensile tail able to pulled him underwater and slapped away several wild boars in battle.
 * Immunity to Death Song: A Thunderdrum bellow is so loud that Thunderdrums tend to be almost deaf, making it the only known dragon which is immune to the Death Song's call. This modulating also prevents sounds from damaging surroundings ("rendering it into a rather calming wave of white noise!"). Because of this, Thunderdrums are nearly deaf. The School of Dragons claims that like snakes they have no outer ear so they are virtually deaf out of water, but they can hear very well underwater like whales and dolphins.
 * Speed: Thunderdrums are able to fly at great speeds in the air, and swim through water like a tornado. Flattening their bodies allows them to skim through the water at even greater speeds or allow for deeper dives for feeding.