"Scauldron, sprays scalding water at it's enemies, extremely dangerous, kill on sight." - Hiccup upon reading the Book of Dragons.
Scauldron is a type of dragon that live exclusively underwater. They are extremely effective swimmers.
Instead of breathing fire, Scauldrons have the ability to scald their victims. This ability comes from sucking in seawater and then heating it in their cauldron-like stomachs before they scald its next victim. This is how they got their name. Scald + cauldron= scauldron. One hit from that hot water will finish off most enemies. They are, like most of the dragons, classified as "extremely dangerous" in the Dragon Manual.
If you want to train a Scauldron, the best way to start is simply to cover yourself in water. Scauldrons are sentimental creatures who love anything that reminds them of home.
This dragon is gigantic. It is a huge sea lizard that walks on four stubby and powerful legs. It's tail is like a fish, helping it to swim. When filled with water, the Scauldron's stomack potrudes out and becomes very round. Its neck is very long and thin, and its head is usually fairly slender with its bottom jaw having a sort of pouch that hands from its chin. Its bottom jaw is very flexible, and it bulges out when filled with water. Its eyes are located near the front of its face, and it has a thin, curving nasal horn. It has peg like teeth that are ideal for catching fish, very sharp, and also happen to be venemous. Two string-like whiskers are connected to the Scauldrons' upper jaw. They have only been seen in three colors: turquoise, green, and pale blue.
In the film
Scauldrons make an appearance in the How To Train Your Dragon film. They are first referred to by Fishlegs who mentions them when talking to the group. They are later shown in an illustration when Hiccup is reading the Dragon Manual after a day of Dragon Training. He takes note of abilities and the various illustrations of Vikings being scalded by it's water, noting that it must be killed on sight.
In Book of Dragons
A Scauldron appears in this animated short. Scauldrons are classified in the Tidal Class, the symbol of this class being a Scauldron. Bork is fishing in his boat and he has a big pile of fish, but a Scauldron keeps eating his fish. Gobber explains that what Scauldrons like more than a fish is, a whole boat of fish. The Scauldron takes some bites out of his boat, and Bork sinks. Later, Bork is seen sketching the Scauldron in a book, which later became- The Book of Dragons.
In Dragons: Riders of Berk
In Dragon Flower, the Book of Dragons speaks of a dragon that feeds on the poisonous Blue Oleander, the "Scauldron". Hiccup thinks its venom would cure their poisoned dragons since the flower doesn't poison it, although the book says nothing on venom. However Gobber tells that they are "60-ft long," with "razor-sharp teeth," they "spit boiling hot water," it has "no fear, no conscience," but what they do have is "venom, and lots of it."
So Hiccup, Stoick, Gobber, and Mildew (who is forced to help against his protests because he caused the entire problem) set out without their dragons to find this beast. When they're some distance from Berk, they throw baskets of the removed flowers into the ocean to attract a Scauldron. It shows up to feast, and Hiccup pours more Oleanders on the boat to lure the dragon closer. Once it bursts out of the ocean and throws the boat in the air, Stoick and Gobber attempt to tie down the dragon's head while Hiccup is tasked to extract the venom. The dragon proves more than they can handle, and Hiccup must instead help restrain it. At this point the only man on board who isn't doing something vital was Mildew, whom Stoick threatens to throw Mildew into the ocean if he doesn't get the venom. As Mildew hesitates with the bucket, the creature suddenly releases a large spray of scalding hot water, frees itself, and after biting one last flower off of Mildew's belt, dives into the ocean.
Everyone looks dejectedly down at the water, wondering how they'll save their dragons now. But then, hearing Mildew's whimpering from the corner, they realize that they have successfully acquired the venom: the scauldron bit Mildew's butt.
- The Scauldron is a big dragon, like the Boneknapper, the Timberjack, Whispering Death, and the Typhoomerang, and not as small as most of the ridable dragons on Berk (Example: Toothless, Stormfly, Meatlug, Hookfang, Barf and Belch, and Thornado.)
- Gobber claims that the Scauldron is sixty feet long. This is most likely inacurrate. Gobber may have seen a smaller indavidual or simply have been mistaken. Monstrous Nightmares grow to sixty nine feet long, and Toothless has a fourty eight foot wingspan. Given these measurements, it is clear that the Scauldron encountered in Riders of Berk is much longer than sixty feet.