Seashocker

The Seashocker is a Tidal Class dragon that appeared in the movie, How To Train Your Dragon 2.

Dragons: Race to the Edge
Seashockers make their first chronological appearance in the episode Shock and Awe. The first Seashocker is a male that got separated from their pod and ended up in the lagoon of Dragon's Edge. They eventually met and interacted with the Dragon Riders, especially Fishlegs, who was mesmerized by the dragon and bonded with them. The Riders tried to help the Seashocker return to the open ocean, but several Scauldrons tracked down and hunted the Seashocker through the lagoon. Fishlegs came to the Seashocker's rescue by joining its heads together, generating an electrical field that pushed the Scauldrons back. Eventually, more Seashockers came to the rescue, and they all swim back into the ocean.

How to Train Your Dragon 2
The Seashocker first appears when Toothless is seen dropped into the ocean. They took Toothless to the shores of the Dragon Sanctuary, where he was picked up by Sailback, while Clawlifter took Hiccup. Their second appearance is during feeding time. The Seashockers can be seen circling a group of fish when the Bewilderbeast spits fish everywhere to feed the other dragons. They have extremely minor appearances throughout the film.

Characteristics
The Seashocker looks similar to a blue, however, it has two heads and has large a wingspan of 15m (50 feet) with two small flippers in front of it, giving it the appearance of a blue colored Manta Ray. The dragon also has small spikes lining its spine and the top of its heads. Their dorsal fins are very sharp and dense, functioning as amazingly powerful blades that are capable of slicing thick sea ices and even the most solid floes. Its necks are incredibly short. In total, the Seashocker's body shape strongly resembles that of a Manta Ray, with wings that extend perfectly straight out. This natural arrangement insures great speed in the air or beneath the waves of an icy ocean. The Seashocker hunts in pods and uses sonar in doing so.

Firepower
The Seashocker is one of the few species to utilize electricity as a weapon. Although it can emit electricity from its mouth, it will be released when it has bitten something, or in a short range just before it nips its target. Their electro-charged bites can take out even the largest enemies. Because of their electro-abilities, rather interestingly, electric eels are regarded as the closest evolutionary relative to the Seashocker, which may be the reason eels are feared by almost all dragons. The episode The Eel Effect, however, suggests the reason dragons fear eels is because of eel-pox and is completely unrelated to the Seashockers.

Electrical Field
As seen in Race to the Edge, Seashockers are be able to generate a field of electricity as a protection around themselves by joining their heads together. An electrical current can be produced by the snout of each head. When the electrical current joins together, it generates a round electrical field, similar to how the Skrill does. The energy released creates a electrical force so powerful, that even large creatures like Scauldrons, after being electrocuted, would be ejected away very quickly, regardless the density of water. It can also apparently eject a human up to approximately 60 feet.

Hunting
Seashockers are also fearsome hunters, similar to  in their lifestyle and intelligence, and are equipped with many weapons including dorsal fins, electric charges, and two heads. Hunting in groups, the Seashocker is an expert in the sneak-attack. If you see its fin in the water, then the rest of its pod has already moved in to attack.

Seashockers are often found hunting in packs or pods and have great teamwork. This helps them to take down large prey easily. They have also been seen herding shoals of fish into a Bewilderbeast's mouth by circling around it.

Echolocation
They use their echolocation to locate its prey in deep water like dolphins, porpoises and whales. The underwater sonar they emit allows them to stealthily detect prey. They use this ability to travel in the deepest depths.

Bioluminescence
The Seachocker also has the ability to glow in deep dark waters where the light doesn't reach thanks to its bioluminescence.

Dorsal blades
Their dorsal blades are very powerful and sharp that they can cut through the thickest sea ice.

Weaknesses
Its shocking ability produces an electric pulse that Scauldrons can sense, allowing them to track it.

Habitat
The Seashocker live in very deep, icy waters, where it can use echolocation instead of sight to hunt prey. It can also use its bioluminescence as an attraction to deep sea fish. But in some occasions, like the dragon's feeding time, Seashockers can appear near the surface where they can help the Bewilderbeast draw fish into its mouth by circling around. In return, some fish are given to them.

Titan Wing
Source: Dragons: Rise of Berk

Titan winged Seashockers have jaws full of spikes and their body is bright yellow. Furthermore, blue stripes streak across their wings and its edges are purple. They have light blue spines on their two necks that merge together to form one row of spines on their backs. They have a cluster of spikes at the tip of their tails.

Trivia

 * Seashockers were originally called Oceanzaps.
 * The Seashocker is most likely based on the Sharkworm from How to Train Your Dragon (series): How to Speak Dragonese.
 * So far, the Seashocker is the only dragon with more than one head that is not a Mystery Class dragon. Furthermore, it is the first Tidal Class dragon to have more than one head.
 * Its name is most likely derived from the sea because it lives in water, as well as the fact that it can shock anything in water with its electrical bite.
 * Seashockers are weak flyers, as their wings are developed to swim underwater. This may be why Valka's Three Seashockers brought Toothless to the shores of the Dragon Sanctuary and gave him to Sailback instead of flying him up themselves.
 * It is the second dragon known to use electricity as a weapon.
 * Seashockers are known to swim in pods. They will encircle a group of fish into a bait ball, allowing other dragons to come in and scarf them up.
 * They must have big hearts, as they are able to dive extremely deep, and any large animal needs a large heart to be able to go down or live in the ocean depths.
 * The theory of it having a big heart might be even more necessary due to the fact that it would need to supply oxygen to 2 brains instead of just 1. This task may be overwhelming even for a big heart, so it may also be possible that they have 2 hearts.
 * They slightly resemble Strafe, a Dinobot from Transformers 4.
 * Seashockers are the natural prey of the Scauldrons.
 * While the chart shows the Seashocker as a large dragon, it is actually a more standard-sized dragon, about twice as long as a Night Fury.