No Dragon Left Behind is the tenth episode of Dragons: Race to the Edge, Season 5. It was released on August 25, 2017.
After being ambushed by aggressive Slitherwing dragons on a new island, the Riders think Stormfly has been poisoned and race to get an antidote. 
After the last battle, the Edge is in pretty bad shape, and the twins have some fun ideas on how to rebuild their hut, even though theirs is the only one to survive. While they're talking, Garff sings in the distance, and the Riders go to find that he's about to consume Smidvarg. Though he's just following his instinct, they decide it's time to find Garff another home. Fishlegs says he's found a great island home for him, so they all escort him there. At first it looks perfect, and the Riders all say their goodbyes, but soon they come across some aggressive and venomous Slitherwing dragons. Stormfly, who has created a strong bond with Garff while he was injured, tries to defend him, but the two dragons and the wild ones disappear in the brush. When they find Stormfly, she's cocooned in amber and Garff is gone. When released, Stormfly starts acting very strange, so Astrid thinks her dragon has been poisoned by the Slitherwings.
The team splits up to find Garff and collect the ingredients for an antidote, while Astrid stays with Stormfly, though she's unable to control her. Fishlegs, Ruff, and Tuff gather the angel fern and tree sap, but struggle on how best to get venom from the wild dragons. At almost getting spit poison at by the Slitherwing they were watching, their dragons drag them away just in time, but without the venom. Astrid is insistent on saving Stormfly and runs toward the aggressive one, eventually punching it with her bare hand, collecting a hand full of venom. Poisoned, she stumbles back to where the others are and collapses, but not before saying to make two doses of the anti-venom.
Meanwhile, Hiccup and Snotlout are trying to find where the Slitherwings took Garff. Snotlout confesses sincere empathy for Astrid, remembering when he thought Hookfang was dying many years earlier and how nice she had been toward him then. They follow the amber trail to a cave where Slithersongs are curled up sleeping and find Garff had sealed himself off from the wild dragons by spewing amber over the entrance of a chamber. They learn that the new dragons' poison coated scales are retardant to Death Song amber, and realize that Garff cocooned Stormfly in an attempt to prevent her from being poisoned.
Back with Stormfly, Astrid wakes up feeling better, but Fishlegs tells her that the anti-venom doesn't seem to be working on Stormfly and he doesn't know why. Thinking her dragon is about to die, Astrid starts crying, and in attempt to save her from embarrassment, Ruff passes the tears off as just dust. The twins then remember when their Great Uncle Magmar was dying and explained his stages of grief. Astrid suddenly realizes that maybe Stormfly isn't poisoned after all, but is merely grieving her friend. Though still sad, Astrid feels better and tries to comfort her dragon, when a song from Garff is heard and Stormfly suddenly perks back up. They follow the songs to the cave and rush in to help fight off the Slitherwings and save Hiccup and Snotlout, their dragons, and Garff. Fishlegs finds another island for Garff to make his home, but the Riders let the two dragons enjoy each other's company a little longer before they head home themselves.
- The episode "Race to Fireworm Island" is referenced when Snotlout remembers when Hookfang was sick and Astrid, for once, was kind to him.
- 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