Green Death

The Green Death, or as it is known in film, The Red Death, is the main antagonist of the book How to Train Your Dragon and DreamWorks' 19th full-length animated feature film of the book adaptation.

Books
In the first book, the Green Death arrives on Long Beach with a smaller Seadragonus Giganticus Maximus (which she eats later on). Hiccup is sent to meet with she and asks if she comes in peace or war as she is the only one who can speak Dragonese.

When Hiccup says his name the dragon shivers subconsciously she seems however that Hiccup did not notice it nor did the Green Death itself. The dragon says he comes in peace but that he s still going to eat them all regardless. The Green Death and Hiccup discuss Singing Suppers, but during the conversation the Green Death moves in to eat Hiccup.

Just as this happens the Green Death yawns, and decides he is too tired to eat Hiccup right now, stating that he should come back in a few hours to be eaten. Hiccup then leaves and tells the tribe that the Green Death, while coming in peace, will still eat them. With the help of the other Hooligan and Meathead boys and their dragons, Hiccup creates a plan to kill the Green Death with the help of a second Seadragonus Giganticus Maximus, the Purple Death, which they trick into helping them.

In the following battle the Purple Death is killed but the Green Death is fatally wounded. In anger, the Green Death swallows Hiccup whole. Fortunately, Hiccup avoids being digested by grabbing and holding on to a Roman spear stuck in the dragon's throat. While inside the Green Death, Hiccup discovers the fire holes (a dragon's source of fire) and blocks them with his helmet. Due to this, the Green Death blows up when she tries to burn Stoick, Hiccup, and Toothless. Her death makes Hiccup a hero in the eyes of his tribe.

In "How to Steal a Dragon's Sword", the Green Death was known as Merciless, the leader of the Dragon Rebellion in Hiccup Horrendous Haddock the First's time. Merciless saw in the future that he was to be killed by a human named Hiccup. He sent Wodensfang to kill Hiccup, but was instead betrayed by Wodensfang when Wodensfang discovers the good in Hiccup's heart. With the Dragon Jewel, Hiccup ordered Merciless to disband the Rebellion and become a loner.

Film
The Red Death first appears when Hiccup, Toothless, and Astrid discover the Dragon's nest, feasting off what his servants feed him. After a Gronckle drops a tiny piece of fish to the Red Death, he emerges and devours the dragon. Then, the Red Death tries to eat Hiccup and his friends when he spots that Toothless has contributed nothing and has humans on his back, but they manage to escape.

The Red Death appears again when Stoick and his vikings attack the Dragon's nest. He attacks the vikings and destroys their ships in the process. Fortunately, Hiccup and his friends arrive and while Hiccup's friends distract the Red Death, he and Stoick save Toothless from drowning as he was caged on one of the sinking ships. Hiccup and Toothless then drive the Red Death into the clouds and conceals Toothless' form. Toothless fires several lightning blasts at the Red Death's wings but they don't have an effect on the monster. Enraged, the Red Death shoots fire in all directions around himself and manages to inflame Toothless's tail. Using as much time as they had left, Hiccup and Toothless lead the Red Death out of the clouds and allowed him to chase them until he attempted to wear a fatal blow at them. However, Toothless fired a lightning blast down his throat, lighting his insides ablaze. The dragon's wings are ripped apart, causing him to fall to the ground and resulting an explosion, killing the Red Death for good.

Abilities
The Red Death primarily uses its enlarged nostrils and hearing in order to hunt down its prey. Its skull is heavily armored and it has a tail specifically designed to smash into objects. It has been shown to have an incredible speed in flight despite it's size, being able to keep up with Toothless for long amounts of time. The dragon also does not have a blind spot, due to it having six eyes instead of two. The Red Death's flame jets are enormous and are powerful enough to take down an entire Viking fleet of ships in just one breath. Like other dragons however, the Red Death cannot hunt efficiently if its wings are damaged and it is just as susceptible to fire on its insides.

Film Developer Description
"This ultimate monster, seen pursuing Toothless and Hiccup, is the most vicious. According to legend, it lives 2,000 years and, before it dies, lays 3,000 eggs. The hatchlings fight each other to the death, a process that can take up to 100 years, until only one survives. “All dragons have a blind spot,” Sanders says. “Except this one. That is one reason we gave him six eyes instead of two. The other reason is that we wanted him to be just generally upsetting. This one is our Godzilla.”"

Trivia

 * The Red Death has some similarities to the Black Mouth from The Little Polar Bear.
 * Both are gigantic beings that have the desire to eat anything they want.
 * Both cause the conflicts of the films they are in (The Black Mouth caused the disappearances of the fish and other animals while the Red Death caused the conflict between humans and dragons).
 * Both are only fully seen towards the end of the films they are in.
 * The Green Death is the first Dragon in the series to actually be evil, the second is the Muddy Bewilderbeast.