Hiccup is determined to finally best Snotlout, who constantly gloats about being the reigning Thawfest champion, but Hiccup's successes begin to make him arrogant and boastful, much to Astrid's displeasure and disappointment. Hiccup and Toothless manage to lure the Skrill into a glacier, freezing it once again. The riders fear how many other slave dragons the hunters have while Viggo assures the riders will pay. The four attempt to work together, but their efforts are hindered by Stoick and Spitelout's constant arguing, and their sons are left to reluctantly take their father's side. They launch their attack and rescue the others, and both sides prepare for their next encounter. Meanwhile, the Hunters, now co-led by the masked man Krogan and a still-living Viggo, make preparations for their next move. The series comes after the short film as the pilot episode and is set about three years after the second season and a few years before the events of , featuring 18—19-year-old characters.
Hiccup develops a diving bell to dive underwater and Changewing Acid to dissolve the chains, but the Hunters' interruption wakes the sleeping Submaripper. Jones Art Brown and Douglas Sloan June 26, 2015 2015-06-26 While gathering supplies, the riders hear of a rogue dragon rider attacking ships and stealing their provisions. Feeling responsible, Hiccup tries to help find a new job for Gobber, however Gobber's slightly eccentric and overenthusiastic personality makes this difficult. Ruffnut sacrifices her long braids in order to finish the support for the wing before the Changewings get them. Johann is able to distract the twins and lead Hiccup to the Sandbuster's lair, where he reveals his deception and demands that Hiccup hand over the lenses. Hiccup and Toothless return from a mission to find Berk mysteriously empty.
Stoick decides to leave, but Hiccup helps him see things from the Jorgensons' point of view and convinces him to return, but when more Singetails arrive, Spitelout decides to abandon the island, stating they will build another storehouse elsewhere. The two escape into the ship graveyard and Hiccup decides to lure it towards Ryker, Dagur, and the hunters to incapacitate it, but his plan backfires and the hunters capture the Skrill. Out of increasing paranoia, Snotlout begins to make reckless decisions that put the other riders in danger and at odds with him when he attempts to develop himself as a worthy leader only to crack under the pressure. Meanwhile, Gobber takes Gothi's place as the village healer, however he is far from good at it. To try and find an alternate method to victory, Hiccup and Toothless travel alone to Storehouse Island to study the Singetail and find behaviors that will give them an advantage in battle, but this attempt quickly leaves Hiccup at its mercy. Feeling he may be denying his sister a chance at lifelong happiness, Tuffnut uses a visiting Changewing on migration to fake his death and allow Ruffnut to go with Throk, but Ruffnut refuses to move on by painting her brother's image on the belly of a Changewing she names Snuffnut and Throk refuses to leave without her and attempts to tame Snuffnut on his own. Meanwhile, the Wingmaidens entrust the egg with Valka, Stoick recovers from his injuries, Mala and Dagur are married, Fishlegs and Snotlout both begin courting Ruffnut, Hiccup decides to destroy both Dragon Eyes to prevent them from falling into the wrong hands and the Riders leave the Edge to return to Berk.
In the commander's quarters of 'The Reaper', Hiccup finds a very mysterious device and after a struggle with Dagur all of the group, apart from Hiccup, are trapped in a cage. Dagur is hunting for the Night Fury that he thought Hiccup battled. It is up to Hiccup and his friends to protect Toothless. Using a Skrill as a diversion, Hiccup and Viggo enter their headquarters where Viggo betrays Hiccup to earn favor with Johann and Krogan once more. Sullivan John Tellegen February 17, 2017 2017-02-17 Dagur returns to the Edge claiming to know the location of Viggo's gold stores, and joins the riders on a mission to take back Berk's gold.
Though Hiccup feels guilty for driving Viggo to make such a move, Stoick expresses confidence that he and the others will always be able to stop him. Sullivan Jack Thomas February 16, 2018 2018-02-16 In order to complete the Dragon Eye and discover the location of the King of Dragons, Johann needs more lenses while Hiccup still needs gemstones to complete his Dragon Eye 2. The trapped Bewilderbeast, with its ability to control other dragons, calls for help from all available dragons, among them are Garffiljorg, the Eruptodon, the Screaming Death, the Frozen Skrill, Thornado, Bing, Bam and Boom and every dragon the Riders ever encountered. Back on the Edge, Astrid works to set up defenses with the twins and explodes into a heated argument with Ruffnut who says that she does not respect others. His obsession quickly lands him in trouble when he and Toothless are stranded on an island inhabited by the hunters and Toothless is incapacitated. A trade takes place, but Gustav decides to stay with Dagur. After Hiccup and Toothless escape, Mildew betrays the Dragon Riders, revealing that Mildew's imprisonment has also been a trick, allowing Alvin to train a Whispering Death.
Following her to Trader Johan's ship, Hiccup interrogates Johan and learns that Heather's island was attacked and her parents killed by Dagur, who she pursues for revenge while stealing supplies to help rebuild. The young Stinger is torn between its pack and the riders, but Hiccup convinces it to go back with its family. But when Alvin and Mildew help him discover what the Screaming Death has been after all along, he comes up with a plan to end the war between the Outcasts and Berk, stop Dagur, get rid of the Screaming Death, and save Berk once and for all. When the baby dragons are forced to live on Dragon Island after nearly destroying Berk, the group learns they can't survive without a parent, so Stoick releases Thornado so he can take care of them, the two parting reluctantly. After her repeated failures, Minden loses hope and confidence in herself and quits being a Wingmaiden, but is inspired by Snotlout not to give up.
Dagur leads Viggo's fleet away and swears to Heather that he will return to answer her questions, leaving his worried sister behind. Hiccup credits Snotlout for a job well done and the twins reward him with a carving of his face in a monument back at the Edge. Jones Jack Thomas June 24, 2016 2016-06-24 With Dagur's information and a map of the location stolen by Johann, the riders send Snotlout and Gobber undercover with Berk's reluctantly lent gold to the hunters' latest dragon auction to rescue the dragons and cripple Viggo's business. One by one the riders are picked off by the rogue until Hiccup and Toothless chase her down and she reveals herself to be Heather, with her new dragon Windshear. Sullivan John Tellegen June 26, 2015 2015-06-26 Hiccup manages to rescue Heather, and though she is still determined to take revenge, Hiccup persuades her to leave it for another day.
The riders and Gothi travel to Glacier Island to retrieve the tooth. Though the Hunters take the island, the riders manage to drive them off with the help of Mala and the Gronkles living on the Edge are recruited to safely return the Eruptodon home. The teens must drive the Screaming Death and the Whispering Death hatchlings away from the village before they destroy Berk. Fearing the possibility her condition may be permanent and her Shield Maiden days are over, Astrid still manages to use her other senses to figure out the Triple Stryke's weakness and finally train it. The twins hold a funeral for Macey back on the Edge, where Tuffnut reveals stolen schematics that leave the riders worried for what 'Project Shellfire' entails.