Dragons: Dawn Of Destruction

Guardians of Vanaheim

Now too aged to fulfilled its duties, the Defenders' Eruptodon passes its mantle of Great Protector to its child and leaves for Vanaheim, the final resting place of dragons that no human has ever seen. The twins disobey Hiccup's orders and follow the Eruptodon to Vanaheim to complete their Viking travel guide, leaving all the Riders stranded on the island and unable to leave thanks to the Sentinel dragons guarding it.

Which have developed a counter-defense for every dragon. Using Mala's advice to look at things differently, Hiccup learns to use the Sentinel's behavior and abilities to his advantage and with help from the Eruptodon, manage to escape, and Hiccup destroys Tuffnut's guide to ensure that no other human will discover Vanaheim.  

After a battle with the Flyers, the Riders discover remnants of Deathsong amber underneath a Singetail's wing, leading them to deduce that Krogan is using a Deathsong to lure and capture Singetails for his Flyers. Worried, the Riders quickly check on Garffiljorg while the others take the injured Singetail back to the Edge for recovery. They discover Garff safe and unharmed, but decide that they must liberate the Deathsong and cut off Krogan's supply of Singetails. Despite Hiccup's orders, Astrid allows Garff to accompany them back to the Edge and to rescue Krogan's Deathsong. Seeing their fortification, they decide to return with reinforcements, but Garff flies in to help the Deathsong upon hearing its cries, resulting in his capture.

Meanwhile, the wounded Singetail wakes up on the Edge and despite Fishlegs' attempts to care for it, it escapes and Fishlegs and Meatlug follow it. After making a plan, they release the captive Singetails only to find the dragons turning on them and forcing the riders to fall back in a cave with no escape. While following the wounded Singetail to the same island, Fishlegs find a hatchery of Singetail eggs and realizes that the Flyers are breeding Singetails. In the cave, Hiccups finds Garff while Fishlegs brings the Cavern Crasher to help dig a new exit and move the Singetail eggs to safety. Once out of the cave, the Riders destroy the Flyers' facilities and free the Singetails.