How to Train Your Viking is a spinoff book of the How to Train Your Dragon book series. It was released in 2012.
It is the day of the Night Fishing Competition. Gobber announces that the winner will get no homework privileges for a week while the loser will have to clean the Dragon Toilets. Toothless is sleeping lazily in Hiccup's pocket until Fireworm teases him about earlier that day. Toothless suddenly remembers that she tricked him into eating an entire barrel full of Nanodragons. This made his stomach bloat and he is now unable to fly. As they are drifting in the dark, Hiccup asks Toothless to fly, but he can't. Toothless then tells him about what had happened. Hiccup and Fishlegs are forced to rely on Fishlegs's vegetarian dragon, Horrorcow who is useless at fishing. When Toothless's belly glows with all the Glow-worms that he had eaten, fish are attracted to it. Fishlegs and Hiccup use a net to haul in the fish, filling their boat to the brim. unfortunately, it also attracts a Darkbreather, who thinks Toothless is a star. Hiccup tells the Darkbreather that if it wants to eat Toothless, it has to swallow the boat. Unfortunately it does, killing itself in the process as the Hopeful Puffin's sail punctures its brain. Drifting like a weird glowing, sea creature, they scare Snotface Snotlout and Dogsbreath, causing them to overturn their boat and lose all their fish. They also scare Gobber, and Hiccup teaches Gobber that everyone is afraid of something, even Vikings. Gobber laughs, and Hiccup and Fishlegs are declared the winners as the Corpse/Boat is full of fish. Snotlout and Dogsbreath are the losers and sent to clean the Dragon Toilets.