Changewing

The Changewing has large wings on its back, horns on its face and an antennae-like appendage on top of each of its eyes. This gives the Changewing a unique appearance. This dragon appeared in episode 18 of Dragons: Riders of Berk.

Description
The Changewing's most noticable attribute is the ability to change the colors of its scales and wings to that of its surroundings, creating an invisible-like effect. Unlike most other dragons, the Changewing can launch concentrated streams of acid at victims. This acid can burn through most, if not all, materials in seconds. Another known feature of this dragon is the unseen ability of hypnotism, only seen in the 2D animation in Book of Dragons so far.

The Changewing's skin is vulnerable to attack, as it is softer due to its color-changing properties.

Changewings nest in large, tall forest in packs. They group together for common goals, or in another word, they are team players, and will stop at almost nothing to remain in possetion of their eggs. Also, Changewings are very curious creatures, and like to mimic everything that they see.

A Changewing's egg has gem-like qualities and are green in base, but its aura glows in multiple colors. Some vikings will mistake these for "Stones of Good Fortune".

In the Book of Dragons
In the Book of Dragons special, they are listed as one of the Mystery Class type dragons, and it is confirmed that not only can Changewings spit acid, but change colors and hypnotize as well. It is also shown that Changewings are very curious dragons. They are seen in a 2D animation where one burns Bork the Bold while he is making a campfire.

In Riders of Berk
The Changewings appears in the 18th episode, Gem of a Different Color. Fishlegs, on his own "secret" island, finds a strange glowing gem. Taking it back to Berk, Gobber identifies it as a "Stone of Good Fortune," causing the citizens to swarm Fishlegs, offering him valuable trades. Overwhelmed, Fishlegs, after refusing to give it to Snotlout, asks Hiccup to help him return it, so that Fishlegs can forget all about it. They, excluding Snotlout, who is secretly trailing, take it to the island, where they find many other of them, and Hiccup realizes that they are truely dragon eggs. Fishlegs returns it, realizing that it must've fallen from its nest and that he had seperated it from its mother. When they attempt to leave, the Changewings trail them, invisible, trying to attack them using their acid. They escape, but Snotlout enters undetected and steals many of the eggs. The next day, Snotlout auctions them off, and the gang tries to convince him something terrible will happen if they remain here. He ignores them and declares, "No returns." The Changewings gradually show up, getting their eggs back, but destroying the village in the process. Stoik and Gobber try to fend them off, but realize that it would be impossible to attack the things they can't see. Hiccup and the gang scramble to return the eggs, and they end up with giving them all back, but the Changewings don't leave. Hiccup realizes Snotlout has kept one and Fishlegs confronts him, displaying anger and strength that scares Snotlout into giving it back. Fishlegs then nervously tries to find them, and the Changewings surround Fishlegs and reclaim their egg from him. Afterwards they roar and terrify the unfortunate viking but leave him completely unharmed. Hiccup later claimed they would need to find one so they could train it, possibly infering they will later appear again.

Trivia

 * The Changewing is one of the mystery dragons in Wild Skies along with the Smothering Smokebreath.
 * Strangely, according to Book of Dragons, the Changewing breathes acid instead of fire while the special shows one burning Bork the Bold.
 * The Changewing is similar to a monkey and a chameleon combined, because a monkey likes to copy things, and a chameleon likes to change its colors.
 * The Changewing's facial appearance is similar to that of the Diplocaulus, a type of extinct, prehistoric Dinosaur
 * The Changewing's size is similar to the Monstrous Nightmare.
 * In the end of the episode of Gem Of A Different Colour, it was hinted that the Changewing could possibly be trained in a later season.
 * In the promo for the season one finale, the Changewing is shown.
 * The Changewing's ability to mimic its surrounding in the episode of  Gem Of A Different Colour,  is different from what's shown in Book of Dragons, its color mimicry in Book of Dragons is fixed on every part of its body while in  Gem Of A Different Colour, Changewings mimic different colours for different parts of its body, even if it's not in contact with Changewings body making it truly invisible with a little distortion.
 * The Changewing's ability to mimic its surrounding in the episode of  Gem Of A Different Colour,  is different from what's shown in Book of Dragons, its color mimicry in Book of Dragons is fixed on every part of its body while in  Gem Of A Different Colour, Changewings mimic different colours for different parts of its body, even if it's not in contact with Changewings body making it truly invisible with a little distortion.