Scauldy first appears in "Free Scauldy", where the gang find him trapped after a shake happened and pinned his wing under boulders. Although initially aggressive towards the teens, he quickly warms up to Ruffnut which allows the others to remove the boulders. As they begin making a splint for him, the gang realize that there wasn't enough rope. Using quick thinking, Ruffnut cuts her own hair off to finish making the splint for Scauldy, allowing him to escape from Changewing island.
Scauldy was initially aggressive towards the gang and absolutely refused any help from them, even to the point of attacking Hiccup, but he took a quick liking to Ruffnut because her hair smelled of fish oil, which smelled like his home as he is a water-dwelling dragon. He is shown to be attached to the ocean, where he lives, as well as becoming protective of Ruffnut. Scauldy is fairly smart and is able to understand Ruffnut when she is talking to him, despite being a wild dragon and (possibly) never hearing human speech. He cares for Ruffnut and also tried to convince her to leave him when the Changewings attacked. He is shown to enjoy Ruffnut singing to him and would look crossly at her when she stops in between. He would also wince or look at her with a scared/angry expression when she sang things like "mash up all your bones"...
Although aggressive, he quickly warms up to Ruffnut after smelling the fish oil Ruffnut puts on her hair to make it look unwashed and greasy, which reminded him of his home. The two become fast friends and they form a strong bond towards each other. Each are willing to risk their life for the another. Ruffnut in particular, sacrificed her hair by cutting it so that her hair may be used to finish the splint for Scauldy. Scauldy is also shown to be concerned for the well-being of Ruffnut as he was trying to convince her to leave him when the Changewings were attacking. Scauldy is shown to be extremely grateful to Ruffnut for saving him and possibly will remember her until they meet again.
Scauldy was originally going to be named "Scalding Painful Death" which was a name made up by Tuffnut, but it was dropped after Ruffnut comes up with the name "Scauldy."
Scauldy lacks the head tendrils that Scauldrons possess.
Scauldy could debatably be the opposing counterpart of Torch.
Scauldy was trained by Ruffnut, Torch was trained by her twin Tuffnut.
Scauldy is a Tidal Class dragon (dwells within the water and sprays water), while Torch is a Stoker Class dragon (dwells on land and manipulates fire and air to attack).
Scauldy was hostile and a danger to the Viking teens, while Torch was civil and friendly from the beginning.
Torch was the one who (partially) saved Tuffnut and Ruffnut was the one who saved Scauldy.
There were rumors that Heather would return in Dragons: Defenders of Berk and train her own Dragon, a Scauldron named Spout. Even though this was eventually deleted, it may have been the inspiration for the character and episode.
Scauldy makes a small appearance in School of Dragons as part of a quest to retrieve Spitelout's fishing rod.