Scrooge, Launchpad and the kids travel to Valhalla to take part in a yearly ritual of keeping the world serpent Jörmungandr at bay. Scrooge wants the kids to see him in action so that one day they can replace him (he does not bring Donald and Della because he does not trust them to work together). They arrive where they are shocked to see that the ritual is similar to that of a wrestling competition. Jörmungandr shape shifts into a humanoid form where he once again announces his intent to face Scrooge McDuck. The kids are surprised to learn that Scrooge, as the Miser, is disliked by the people of Valhalla while Jörmungandr is seen as the people's champion. Dewey is put off by this as he feels that they should be viewed as heroes.
Meanwhile, Louie steps out to make money off of the fight's merchandise while Launchpad and Huey take over as announcers after Scrooge accidentally knocks out the previous one. Huey cannot fathom the frantic pace of wrestling while Launchpad is able to do so effortlessly, causing Huey to feel like he is becoming the Launchpad of the situation. Scrooge faces off against Strongbeard, a fighter whose beard hairs allow anyone to become strong. Scrooge manages to easily defeat him, but when Dewey tries to defend him from the crowd's booing, an audience member tosses a chair at him. Scrooge defends him, but injures his back.
Scrooge realizes that the kids need to take part immediately and asks Webby to replace him. Dewey instead steps up as Champ Popular with the intent to get the crowd to like him. Due to the next fight being a tag team effort, both go up. Despite Dewey's efforts, the crowd still hates him because of his obnoxious personality and misinformed tastes. They face off against Hecka and her dog Fenrir where Dewey fails to be effective in fighting (he is more concerned with winning over the crowd) while Webby manages to hold her own. Dewey and Webby end up losing with Jörmungandr offering to face off against the entire earth team which Scrooge accepts while Dewey solemnly hides from everyone.
Scrooge comforts Dewey and admits that not everyone is cut out for being defender of the Earth before revealing that he called for backup. Mrs. Beakley arrives as Shield Maiden and she and Webby take on Jörmungandr, followed by Scrooge and Launchpad, as Captain Crash, but all four are defeated. Both Dewey and Huey talk about their predicaments when Louie comes in and tells them that the world is ending due to Jörmungandr winning. He tells the two that Huey is good at learning from things while Dewey never cares about what others think. The three brothers head off to save the world.
Dewey takes on Jörmungandr despite getting beaten severely. When Jörmungandr boasts his superiority over Dewey, the crowd begins to turn on him. Strongbeard and Hecka begin to side with Dewey, resulting in the former giving a large piece of his beard to him to face off against Jörmungandr. Dewey uses his newfound strength to easily beat him and saves earth. As he is offered the championship belt, Scrooge heads up to congratulate him and steals the belt for himself. Catching on to the game, Dewey and Scrooge have a friendly face off.
- David Tennant as Scrooge McDuck
- Danny Pudi as Huey Duck
- Ben Schwartz as Dewey Duck
- Bobby Moynihan as Louie Duck
- Kate Micucci as Webby Vanderquack
- Toks Olagundoye as Mrs. Beakley
- Beck Bennett as Launchpad McQuack
- Kristofer Hivju as Jörmungandr
- John DiMaggio as Strongbeard
- Eric Bauza as Announcer
- Jörmungandr was first mentioned in the episode "Last Christmas!" while Scrooge was describing his responsibilities throughout the year, one being "keeping the world-eating serpent Jörmungandr at bay."
- Hecka, is a reference to Hela of Norse mythology. Her name is a place on the casual replacement of the word Hell with Heck.
- In a slight nod to the episode "Maid of the Myth" from the classic DuckTales, Mrs. Beakley is seen wearing a Viking outfit for her wrestling uniform.