The Iron Gronckle is the second episode of Dragons: Defenders of Berk and the twenty-second episode overall. It aired on Cartoon Network September 26, 2013. The plot focuses mainly on Meatlug and Fishlegs as terrible trouble arises when Meatlug eats magnetic rocks and produces Gronckle Iron. It is preceded by Live and Let Fly and is succeeded by The Night and the Fury.
The Riders an Outcast ship who somehow outran them. Hiccup asks how, and Snotlout mocks Fishlegs that his dragon is the reason for being too slow. Fishlegs harshly accepts Snotlout's point. Fishlegs tells them to continue their search while they circle around to patrol the cliffs and the surrounding islands. Fishlegs sadly heads off. Down at the standing rock to where they all rallied, the Outcast Ship hides there and Savage is actually leading them as they quietly set sail. Fishlegs and Meatlug are stationed for a while to their feeding spot, and they are depressed after hearing what Snotlout said. In order to cheer them up, Fishlegs and Meatlug quickly dig in, as Meatlug eats dozens of random rocks and Fishlegs eats berries and goes faster and faster. Hours later both of them don't feel well especially Meatlug. They head to Gobber's workshop and seek help to figure out what's wrong with Meatlug. Fishlegs explains Meatlug hasn't spewn lava for a long time now and is still unable to do so. In order for her to spew lava, Gobber tickles her stomach with a feather and in seconds Meatlug vomits lava all over the floor forcing the two to stand on higher ground. Fishlegs is suspicious Meatlug never spews that much lava and the lava forms with a different color.
Meanwhile, Savage and some Outcasts go check on the secret cavern where the Whispering Death eggs were planted. As soon as they check all the eggs have been broken and dozens of Whispering Death babies fly around and creating tunnels. However, one Outcast spots an unnaturally sized Whispering Death egg that started bigger than the other egg, Savage never saw one that size before and above them sees a huge tunnel never seen before. A large roar is heard and Savage and the Outcasts walk away and leave it alone.
Back on Berk, the Riders failed to find the Outcast ship. Gobber arrives to tell Fishlegs the lava Meatlug spewed earlier on made it out to a sword because he was tired of waiting for it to cool. Gobber calls the material Gronckle Iron and the sword made of Gronckle Iron is incredibly lighter but is incredibly impenetrable. For example, Gobber uses it to break Snotlout's sword in an instant. The Riders are amazed and wanted their weapons, helmets, and other things to be made out of Gronckle Iron. Hiccup also wants his shield to be made out of Gronckle Iron. As soon as the news breaks out of this new material, the entire village lines up and wants their things to be made out of Gronckle Iron too.
At Gobber's workshop, Fishlegs gladly helps Gobber makes things out of Gronckle Iron by making Meatlug spew as much Gronckle lava as possible. The town appreciates Meatlug and Fishlegs for the first time in their lives, keeping them supplied with things made out of Gronckle Iron. Meanwhile, Hiccup completes his upgraded shield and asks Fishlegs what kind of rocks Meatlug ate, but Fishlegs keeps it a secret and doesn't reveal it to anyone including Gobber. Astrid informs Hiccup another Outcast ship is spotted and requests they leave immediately, Fishlegs stays behind and tells Hiccup to go on. But Meatlug ran out of lava to spew and the town is worried and slowly impatient as no Gronckle lava spews out. With little time before a riot starts, Fishlegs has no choice but to let Gobber come with them to pick up the exact rocks Meatlug ate earlier. Fishlegs reveals he has no idea what rocks Meatlug ate after eating so much in a frenzy. Gobber suggests they pick up as many random rocks in the area as possible and try it one at a time with Meatlug. He's sure Meatlug will spew the perfect lava later on.
At the Academy, the Riders failed and wasted time to find the Outcast ship again. They suggest they need Fishlegs and Meatlug because every Rider has a role and feel sorry for mocking them for their speed. Snotlout blames Hiccup for letting Fishlegs go. Hiccup thinks he's the reason why Fishlegs isn't here and heads out to find him.
Back at the Workshop, Gobber and Fishlegs fed Meatlug with each kind of rock but all attempts failed. Either the lava spewed out is weak or overheats herself. The Riders arrive and try to call him, but as soon as they do, the town rages on against Fishlegs. Sooner or later Fishlegs is in deep trouble. Fishlegs come up with an idea, by feeding Meatlug each type of rock at the same time, they wait for something to happen. Every metal object flies towards Meatlug, revealing the combination of rocks she ate made her skin become magnetic. Bigger metal objects fly towards her, and she panics and runs for her life. As soon as she runs through town, metal objects follow her. Hiccup and Toothless shoot away all the metal weapons following her. Snotlout and Hookfang fail to stop her, as Fishlegs tells Hookfang to heel. Meatlug runs deeper through the forest. Hiccup and Toothless follow her overhead.
Meatlug hits a dead end cliff. Hiccup reaches her and tries to calm her down and hold her still. Meatlug slowly backs away. Fishlegs arrives to warn Hiccup (who wouldn't listen for a moment) he doesn't realize his metal leg is attached to him and gets dragged away when he gets in range of the magnetic attraction. Meatlug panics and unintentionally takes Hiccup with her and flees, with no idea of where they'll go. Meatlug and Hiccup are now far out to sea. Fishlegs has no choice but to ride Toothless, but he never rode or flew a fast dragon. The two have trouble flying, as Fishlegs is scared of Toothless being too fast. But Fishlegs faces his fear and rides Toothless perfectly by using maneuver tactics. Fishlegs reaches Hiccup and they awkwardly greet each other. Hiccup apologizes Fishlegs for leaving him earlier that day, but Fishlegs tell him to keep quiet in order for him to concentrate. The two spot an Outcast ship dead in their sites and prepares to fire on them. Hiccup tells Meatlug to dive and head straight pass near the ship. The moment Savage orders the Outcasts to fire, the ship tumbles and their weapons timber and float toward Meatlug. With little time to spare, Fishlegs tickles Meatlug's stomach with the feather and barfs out the magnetic rocks she ate. The metal objects fall, including Hiccup, who falls incorrectly on Toothless. Meanwhile, Savage brags it's not over but gets interrupted when the heavy metal objects fall on their ship busting a hole and sinking their ship.
The two happily head back to Berk. Fishlegs quits helping Gobber make more Gronckle Iron as he furthers his responsibilities to the Academy. Gobber understands and gives him the first sword he made for himself and the first and last one to be made of Gronckle Iron. Gobber states he gave his sword to Fishlegs after he destroyed the Outcast Ship earlier on. Gobber also gives Meatlug a pair of earrings for her bravery too. Hiccup and Toothless arrive and inform Fishlegs they need them. Fishlegs and Meatlug are happy hearing they actually needed them for the first time. The Riders fly altogether and finally bond as a team.
- This is the first episode that the Outcasts appear without Alvin.
- One of the Viking's name is Gunnar. This is the same name for those who had Astrid, and chose boy, on the Viking Personality Test that was on the Legend of the Boneknapper Dragon DVD.
- This episode has a similarity to How to Break a Dragon's Heart. When Toothless ate Stoick's "magic" stone and would stick to metal objects.
- Stoick did not appear in this episode. This is the first time he didn't appear in the series.
- This is the second time Meatlug unintentionally kidnaps Hiccup. The first one was in Gift of the Night Fury.
- It is revealed in this episode that Fishlegs has Binge Eating Disorder (eats when depressed).
- The exact formula behind Gronckle Iron discovered as part of a quest in School of Dragons.
- New metal alloy is discovered: Gronckle iron, but the formula is still unknown.
- Hiccup finishes his shield, using Gronckle Iron.
- The Screaming Death's existence is first hinted at.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Chris Edgerly as Gobber the Belch
- Christopher Mintz-Plasse as Fishlegs Ingerman
- Andree Vermeulen as Ruffnut Thorston
- T.J. Miller as Tuffnut Thorston
- Zack Pearlman as Snotlout Jorgenson