The Green Death is a giant dragon controlled by Ratigan in the Spongebob version of the Great Mouse Detective. Due to the robot queen plan having been canceled due to Scroopfan's regular story changing, the villain leage desided to go with a simpler and less sneaky plan to simpley invade Buckingham palace and congure london by force. When that was in danger of failing before it could start as well, Ratigan now chases Hiccup and Toothless for ruining his plans on a Green Death, claiming to be another member of the same spieces of the one that was first encountered in How to train your dragon, what with Fidget now being reformed and no longer being pushed off the blimp like before. The Green Death originates from what is mentioned above. this creature is also posably Ratigan's personal Mount.
In the movie adaptation of the original book, the Seadragonus Giganticus Maximus is renamed the Red Death. It serves primarily as the movie's indirect main villain/antagonist. Initially seen dwelling in the volcanic interior of the Dragons Nest, the Red Death acts as a parasite, sustaining itself off of all the livestock its 'dragon servants' bring it as a meal. It eats anything that contributes little to nothing, as seen with a sole Gronckle who donates a single fish, and anything that gets in its way will also become eaten, as seen when a Hideous Zippleback got in its way when the dragon was attempting to escape as the dragon was trying to eat Toothless, Hiccup, and Astrid without the dragon noticing this. The dragon almost takes the oppurtunity to eat up Toothless when it spots that he has contributed nothing and has humans on his back. Hiccup, Astrid and Toothless barely manage to escape. In the movie its gender is debatable. Astrid refers to it as a "Queen" but she is speaking metaphorically comparing the dragon mound to a bee hive. However Hiccup calls him a he when he say to Toothless,"Well he can fly!" So the Red Death is most likely a male dragon since Hiccup says he is and his counterpart in the books is also male.
The Red Death isn't seen afterward until the climactic battle between it and the Vikings. Stoick arrives with the rest of the village on the island housing the Nest and succeeds in scaring off the dragons that serve the Red Death. Enraged at the Vikings, the Red Death soon breaks through the mountainside to destroy them. The teenage Vikings soon arrive on their own dragons to fight off the beast. While the other Viking teens distract the Red Death, Hiccup nearly drowns after trying to save and unchain Toothless on one of the boats which the Red Death had set fire to. Luckily, both of them are saved by Stoick and Hiccup, along with Toothless, takes off to confront the Red Death.
After circling the island once, Toothless begins to anger the Red Death by launching a fireball at the monster's side. The enraged dragon then pursues Toothless and Hiccup into the skies where Hiccup decides to use the heavily clouded sky as a cover. Toothless then attacks the Red Death in the clouds with a barrage of fireballs aimed toward its thin wings. The Red Death angrily sets the entire sky, as well as Toothless' makeshift tail, on fire. After seeing this, Hiccup and Toothless decide to finish the dragon once and for all by skydiving towards the island with the Red Death hot on their heels. With the beast just above them, Toothless launches a fireball directly into the flammable gases within the Red Death's mouth. The gases ignite violently inside the Red Death as it discovers that it cannot pull out of its skydive with its wings in tatters. The Red Death crashes into the island and combusts in a bright, fiery explosion.
The victory comes with a cost. As the dragon explodes, Toothless collides with it's huge tail and sees Hiccup fall off his back and into the fire. Even though the Night Fury is able to save his human friend's life, Hiccup's left leg is burned and mauled beyond repair. He eventually gains a prosthetic as a replacement for his limb.
The Red Death primarily uses its enlarged nostrils and hearing in order to hunt down its prey. Its skull is heavily armoured 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 succeptible to fire on its insides.