Shattermaster

Shattermaster is a Gronckle who was ridden by Dagur in Dragons: Race to the Edge. Dagur was hoping for a Skrill or a Night Fury, but was a bit displeased upon seeing that he'd be riding a Gronckle. In fact, he initially thought that Shattermaster was going to be breakfast for a more powerful dragon. However, he completely changed his mind upon seeing Shattermaster's abilities.

Meeting Dagur
In "Family on the Edge," Shattermaster first appeared as Dagur's new dragon. He was chosen by Hiccup, mainly because he thought it would be safer for Dagur to ride the "slowest and least dangerous dragon" he could find. At first, Dagur refused to train Shattermaster, claiming he was "beneath him". However, Dagur accepted him soon after his failed attempt to mount him. The duo then enthusiastically began training with Hiccup, and later Fishlegs. Shattermaster was said to be a fast learner, as shown by his mastery of the Inverted Gronckle Drop. When Dagur was locked up after being accused of spying for the hunters, Shattermaster broke them out, which prompted Fishlegs to comment on how well they had bonded. Upon reaching the hidden shipyard, Dagur and Shattermaster charged into battle and laid waste to the hunters' fleet. Unfortunately, Shattermaster and Dagur were shown to have not survived and were presumed dead.

Being Rescued and Fighting the Dragon Hunters
When Hiccup and Heather discover that Dagur is alive in "Saving Shattermaster", he reveals that he's been undercover in order to save Shattermaster, who was captured by the Dragon Hunters.

After an agreement between the three and a short research, Hiccup, Heather and Dagur go to rescue Shattermaster. They are successful, as they manage to free other Gronckles too. However, the Dragon Hunters follow them, so Dagur and Shattermaster distract them while Hiccup and Heather get the dragons to safety.

Dagur and Shattermaster return in "Gold Rush", when the riders go to retrieve Berk's gold that was lost to Viggo. While trying to break a dragon-proof door, Shattermaster uses a new move that Dagur calls Shatter Skater. He then later helps in rescuing the dragon riders using a move called Flying Shater Skater, which he performs with the help of Windshear. At the end of the episode, he leaves with Dagur, Heather and Windshear for Berserker Island.

Shattermaster takes part in Hiccup's mission to retrieve the Dragon Eye from Viggo in "Shell Shocked, Part 1". However, they found the island destroyed, so Hiccup sends Dagur and Shattermaster back to Barserker Island. He later appears when the Shellfire attacks Berserker Island, flying away from the island.

Shattermaster helps defending the Edge in "Shell Shocked, Part 2". He and Dagur save Sleuther from the Dragon Hunters. However, he is badly hit by a boulder in the process. Dagur then promises to defend him to the death. Fortunately, Sleuther comes and fights the Dragon Hunter with Dagur riding him. After Hiccup arrives, he tells Dagur to look after his dragon as he needs help.

For reasons unknown, Shattermaster is not present in the fifth season, with Sleuther instead serving as Dagur's dragon.

Mentioned by Dagur
"I'll help Fishlegs get Meatlug back on her feet in fighting shape in no time. Don't worry about her; she's a fighter, just like Shattermaster."

- Dagur in School of Dragons

Despite not appearing ingame, Dagur does reference Shattermaster in the expansion Rise of Stormheart.

Personality
Shattermaster is shown to be hyper-energetic and a truly friendly dragon. Much like Gustav and Fanghook before them, Shattermaster formed a strong bond with Dagur after only a day of training with him. He's also shown to be quite protective of Dagur, as seen when Astrid threatened to harm his rider if he betrayed them. Shattermaster doesn't even hesitate risking his life alongside his rider to protect the Dragon Riders and Heather.

Dagur the Deranged
He met Dagur when he was given as gift from Hiccup because Hiccup wanted Dagur to have the slowest dragon just in case Dagur was lying about changing his ways. Though Shattermaster has shown to have great trust in Dagur as he was willing to defend him from Astrid when she verbally threatened him, and this was after only a few short hours of being together. He was even willing to sacrifice himself with his master in order to protect their friends. And Dagur has come to care for the Gronckle in a very real way.

Hiccup Horrendous Haddock III
He might have been trained by Hiccup as he was called upon when Hiccup whistled. And he may have had a good bond with Hiccup since he gets so excited to be with humans.

Toothless
Shattermaster might have some good bond with Toothless as Toothless does his best to get along with many dragons. Toothless trusted Shattermaster to carry Hiccup back to base without him to fetch a spare leg.

Fishlegs Ingerman
He might have been thankful to learn some experience with Fishlegs as he has a lot of experience with Gronckles. He's definitely thankful when Fishlegs feeds him a basket full of fish after he and Dagur had gone a considerable amount of time without being able to eat.

Meatlug
Like Toothless, Meatlug also gets along with many dragons as she loves to get along with any dragon she meets that are good. She enjoys helping Shattermaster learn new tricks to do with his rider.

Astrid Hofferson
Shattermaster might have some respect for her after she threatens his new rider, and is quick to defend him from her if needed.

Stormfly
Shattermaster might have been thankful after learning some experience from her, but was willing to defend his owner when Stormfly was threatening his owner along with Astrid.

Heather
Shattermaster's first encounter with Heather was when he and Dagur were trying to get away from her, so he worked with his rider to confuse and disorientate her. But later, he easily picked up on Dagur's affection for his sister, and appears to accept Heather as a friend, even becoming protective of her similarly to Dagur's protective behavior toward her.

Windshear
Windshear didn't seem too fond of Shattermaster at first, after he butted her in the stomach mid-flight. But the two seem to have reconciled when they see their riders' affection for each other. They even learn to work together to pull off Dagur and Shattermaster's new trick; the Flying Shatter-Scatter; as she carries Shattermaster in flight with her tail and flings him toward a target.

Abilities and Skills
Intelligence: In one day, Shattermaster was able to have been trained quite fast, even with a trainer as inexperienced as Dagur. He was able to help his owner by using the chain to make the dragon hunter trip over it easily.

Strength and Combat: He has proven to be very strong and fights like a typical Gronckle. He's even strong enough to briefly incapacitate Windshear with a tail bludgeon to the stomach.

Speed and Agility: Shattermaster has been proven to be quite fast for a typical Gronckle. He is even shown to be agile enough to dodge Windshear's attacks and was able to do a back flip to dodge a barrage of the Dragon Hunters' arrows.

Inverted Gronckle Drop: Inspired by nearly falling out of the sky on his first flight with Dagur, Shattermaster was able to master a modified version of Fishlegs and Meatlug's Gronckle Drop. It's an effective yet borderline insane maneuver, not unlike Shattermaster's rider.

Endurance and Stamina: Shattermaster has proven to have high endurance when he was hit by a large boulder and was still able to walk, despite being unable to fly. His stamina is also as good as any other Gronckle, as he is capable of flying for long periods of time.

Shatter Skatter: This is a move that Dagur and Shattermaster have evidently come up with between Saving Shattermaster and Gold Rush. It is a battle move where Shattermaster curls up into a ball and rolls at high speed and then uncurls seconds before he hits his target. It is capable of breaking through dragon-proof metals.

Flying Shatter Skatter: This new skill is a combined effort between Windshear and Shattermaster. In this move, Windshear uses her tail to hold Shattermaster and then tosses him towards a target. Like in the normal Shatter Skatter, Shattermaster then curls up into a ball and rolls at high speed and then uncurls seconds before he hits his target. Also, like the regular Shatter Skatter, this move is capable of breaking through dragon-proof metals.

Trivia

 * No other known Gronckle has the same coloration as Shattermaster.
 * It is possible that Hiccup trained Shattermaster before giving him to Dagur, due to his friendly behavior towards them.
 * Shattermaster is one of only two dragons that can break dragon proof metal, with the other being Grump.
 * It is unknown why Shattermaster was absent in Season 5.
 * A speculated reason is that he died from the injury he sustained in Season 4.