Eruptodon

The Eruptodon is a large Boulder Class dragon which appears in School of Dragons and in Dragons: Race to The Edge, Season 4.

Physical Appearance
Eruptodons are large dragons that have a round body and quite a long tail. Their wings are relatively small and their heads are as big as their bodies. Their front legs are very small compared to their hind legs and they have several big, spiky lobes along their backs and tails. Its body is covered with thick spineless, volcanic rock armour made of cooled lava. Its eyes are protected by welder goggle-type lenses to help withstand the intense heat.

Behavior and Personality
The Eruptodon is the first known dragon species to eat lava. It prevents volcanic eruptions by residing in the magma vent of a volcano and eating overflowing lava. As such, Mala and her people worship this dragon for protecting their village. She mentions that the Eruptodon never allows the lava to flow too far down, hinting that the dragon may have a protective streak over the whole island.

If an Eruptodon has not eaten for a long period of time, it will go into a feeding frenzy and will eat any lava it can find. If it can not find any, it will die. It does not require an active volcano to eat, as, if sufficiently motivated, it will tunnel into dormant volcanos to access the lava, causing them to erupt in the process. Nothing, except lava in another direction, will stop them once they are in a feeding frenzy.

Lava-Proof Skin
Due to its lava-proof hide, the Eruptodon can live in a heated volcano without being harmed.

Strength
The Eruptodon has been shown to be very strong, as the Great Protector was capable of lifting the heavy metal Diving Bell as well as the weight of Throk inside of it.

Saliva
The saliva of an Eruptodon is extremely resistant to heat. This saliva can be used to protect people who are trying to enter a volcano like the one on Caldera Cay.

Firepower
The Eruptodon's fire comes from the lava that it eats. It fires this lava in a series of small fireballs. These fireballs can can cool down into hot rocks and can even construct a path that can be walked upon, albeit painfully, as seen in Saving Shattermaster.

Digging
The Eruptodon is capable of digging into the crust of a dormant volcano in order to access the lava within.

Lava Eating
The Eruptodon's main food source is lava. Because of this, it is able to stop volcanic eruptions by eating the lava and keeping the volcano stable. Even baby Eruptodons are shown to be capable of doing this. It is due to this ability that the Eruptodon is worshiped by the Defenders of the Wing.

Weaknesses
If an Eruptodon does not consume lava for a long period of time, it will die.

The Eruptodon only produces one egg during its lifetime. This could cripple the species, as it would make their population very small. If the egg of an Eruptodon is not immersed in lava like the kind inside the volcano on Caldera Cay, it will harden until it is like stone and the baby inside will die.

Season 3
First mentioned in "Defenders of the Wing, Part 1", the only Eruptodon known to exist was found on Caldera Cay, an island ruled by Queen Mala of the Defenders of the Wing. It was known as the Great Protector. However, it was taken by the Dragon Hunters when Mala was interrogating Hiccup and his group.

Season 4
In "Defenders of the Wing, Part 2", the Great Protector (a female Eruptodon) was captured by Viggo and Ryker. She was aggressive at first, then became more interested in her own survival. Mala is worried about the Eruptodon, and said that Eruptodons must constantly eat lava, or they will starve to death. But Viggo plans to use the dragon to destroy Dragon's Edge by having her feed on the lava of the Edge's dormant volcano to cause an eruption. However, Mala and the riders arrived in time to stop here before she could produce a volcanic eruption by feeding her with Gronkle lava and get her back to Caldera Cay.

Trivia

 * It is the first dragon (not created in a video game) which makes its first physical appearance in a game before it does in the show.
 * It is the second dragon with lava-proof skin, the first being the Red Death.
 * It is the second dragon that is seen as a statue before being physically seen, the first one being the Grapple Grounder.
 * The Eruptodon is very phoenix-like because of the way it lives for generations then lays a single egg before it dies.
 * This and the Dragon Hunters would be the top contributors to making it an endangered species.
 * It's very likely that when the Eruptodon fires its balls of lava, the lava mixes with the Eruptodon's heat-resistant saliva, which can be the reason why its lava blasts can be cooled down to form hot rocks very quickly.