|“||While on night patrol, Stoick is ambushed by the Flyers and gravely injured, leaving Hiccup torn between his duties as a son and as the Riders’ leader.||”|
Stoick and Skullcrusher venture alone for an evening patrol of Berk. They are suddenly caught off guard as several Dragon Flyers ambush them and both Stoick and Skullcrusher are severely injured in the attack. Luckily, the A-Team arrived, fends off the Dragon Flyers, and rescue them to safety. When word spreads of Stoick's unconsciousness due to his injuries, Hiccup races home and is devastated to see his father's condition, resulting in him being too grief-stricken to notice his fellow Riders. With no chief to take care of the village, the Riders and lead Vikings congregate as they discuss the fate of Berk with no leader. Spitelout and the Vikings agree that Hiccup must take up chiefdom in Stoick's absence. Gobber and Astrid attempt to deliver the request to Hiccup. However, Hiccup strongly rejects the offer as he reasons that he needs to be with his father until he hopefully recovers.
Hours later, Hiccup has trouble sleeping as his father’s words echo in his dreams and decides to stay in the Great Hall, as he is torn as to what his response should be in the aftermath. The Riders also arrive in the Great Hall to comfort him. Astrid tries to dissuade Hiccup from believing that he is to blame for what has unfolded but the Twins argue otherwise, claiming if the Riders never left he would've kept his father safe but on contrast Berk would've gone into a state of "full Loki" and end up in the same situation with Johann. They envision their alternate reality, where they go back to the time where they first began deploying pranks on Berk and soon escalates that eventually, everyone in the entire village pulled pranks on each other, leaving Berk defenseless and oblivious that Johann and his lackeys are able to take over Berk in a single blow.
Fishlegs suggests a different view of what would happen if they all stayed, whereby Berk eventually grows to immerse themselves in a state of peace and tranquility in which wars will be pointless resulting in relations with Johann, Viggo, and Dagur. But Snotlout interjects that in the end, they will eventually turn on against each other, as he believes it's in a Viking's nature. He then presents his own point of view where he believes that he'll eventually be promoted to a legendary Official Weapons Inventor, where he wields his greatest super-weapon and becomes a warrior revered by all of Berk, including his father and Astrid.
All their stories are viewed by the Riders to be ridiculous and they dispute which is the more likely scenario. Frustrated, Hiccup snaps, telling them all their predictions are pointless and instead that all the events that led up to the present are because of his fatal shooting of Toothless years ago, and he blames himself believing that decision endangered his father. He walks out of the Great Hall in despair. For a long moment, Hiccup isolates himself sitting at a cliff edge at night. Toothless joins him, despite hearing that his Rider seems to regret his actions that resulted in their friendship. Hiccup apologizes, reassuring Toothless that he never meant it to be true. Astrid follows and tries to talk some sense into him. Astrid asks Hiccup to envision himself what would he be like if he never did shoot Toothless in the first place.
The scene then flashes back to the moment in the first film, where a young Hiccup is moments away from pulling the trigger. When Toothless comes into range, he fires, and then the bola misses him. History changes from that point on, as a few years later, Hiccup still works at Gobber's blacksmith, with the only companion being Fishlegs, who is now interested only in studying plant life, and that Snotlout is admired by Stoick for his record of killed dragons and prepares to woo Astrid in marriage. Stoick confronts Hiccup demanding that he finally makes his first dragon kill out at the forests and that he can't return unless done so. At the cove, Hiccup awaits for the dragon he will confront, which turns out to be a Night Fury. While busy taking a drink, Hiccup tries to capture it with a net but clumsily fails. Fortunately, Toothless suddenly gets tangled up in the net, enough to be immobile. When Hiccup takes out his knife and lifts it, he still couldn't bring himself to kill it so he frees it. Just when the pair begins to go their separate ways, a Whispering Death emerges and attempts to attack Hiccup. Toothless dives in and rescues Hiccup, but in the process, Hiccup latches on Toothless's body while Toothless prepares to take off with the Whispering Death in pursuit.
Their chase attracts the attention of Stoick and Gobber, who is shocked to see that Hiccup is riding the legendary Night Fury and they set foot to save him. One of Toothless's tail fins gets shot by the Whispering Death, rendering them flightless and they crashed back into the cove. Toothless is momentarily unable to fight back, and the Whispering Death prepares to seize the moment. Hiccup bravely attempts to divert the dragon's attention to him, but he gets brutally struck with the Whispering Death's flames and loses consciousness. Seeing his bravery, Toothless tries to avenge him as he protects Hiccup from being finished by the Whispering Death. Help eventually arrives, as Stoick and Gobber overpower the dragon and leaves defeated. Stoick is prevented from killing Toothless when he realizes that the dragon kept his son safe. Days later, Hiccup recovers but with a prosthetic leg due to the attack, and that Toothless is allowed to enter Viking society with his tail fin repaired by Gobber. Stoick presents Toothless as not a threat but a hero to Berk, and Hiccup and Toothless are praised by the villagers including Astrid. Stoick finally declares an end to hostilities to all dragons.
The scenario finishes and Hiccup and Astrid realize that the other Riders were listening in, with the Twins complaining why did the entire scenario still had the same results as it did in their own reality. They clarify that no matter how things have gone, Hiccup, Toothless, and the rest of them are bound to be in the state they are now. Hiccup finally is relieved of his self-loathing as he accepts that none of his actions are to blame. He goes on to have one final visit with his father, trying to assure him that he won't give up and that he will continue to fight back against Johann and wishes that he pulls through his condition, for the village and his sake. Just as he prepares to leave, Astrid interrupts and urgently requests Hiccup outside. Hiccup finds an injured Heather, now laying in Fishlegs’s arms, bringing Hiccup dire news that the Dragon Flyers have invaded Vanaheim.
- Astrid's "what if" scenario has several references to the books.
- Hiccup and Fishlegs are still best friends.
- Snotlout continues to bully Hiccup.
- Stoick is quite proud of Snotlout's abilities and pressures Hiccup into following them.
- This is the second time a flashback from the first movie appears in the series. The first time was during "Viking for Hire".
- Toothless's Nemesis makes its first appearance since "What Flies Beneath", although only in a "what if" future.
- The "what if" scenario for Snotlout and the Twins are very similar to the stories they tell in Burning Midnight.
- This is the first time we see Toothless with both of his tail fins intact.
- The Whispering Death's fire should not have destroyed Toothless' left tail fin in Astrid's "what if" scenario, as dragons are fireproof.
- Jay Baruchel as Hiccup Horrendous Haddock III
- America Ferrera as Astrid Hofferson
- Christopher Mintz-Plasse as Fishlegs Ingerman
- T.J. Miller as Tuffnut Thorston
- Andree Vermeulen as Ruffnut Thorston
- Zack Pearlman as Snotlout Jorgenson
- Nolan North as Stoick the Vast
- Chris Edgerly as Gobber the Belch
- David Tennant as Spitelout Jorgenson
- Lucas Grabeel as Gustav Larson
- David Faustino as Dagur the Deranged
- Mae Whitman as Heather
- Barf and Belch
- Krogan's Singetail
- Toothless' Nemesis
- Night Fury
- Deadly Nadder
- Monstrous Nightmare
- Hideous Zippleback
- Terrible Terror
- Whispering Death