The Inferno, also known as Dragon Blade, is Hiccup's main weapon in the second film.
As Hiccup began exploring further away from Berk, he began to discover more species of dragons and so created the Dragon Blade, also known as Inferno. It was created for the purpose of pacifying any wild dragons that he and Toothless came across. Hiccup received the idea of the Dragon Blade for the first time when he noticed the qualities of the saliva of a baby Monstrous Nightmare, during Berk's first Snoggletog with the dragons.Gift of the Night Fury It is unknown when the Dragon Blade was forged, but it is shown in the second film that Hiccup uses it to train and pacify wild dragons he comes across during them on his travels.
Hiccup first used the Dragon Blade when Stormfly had been captured in a net, fired by Eret, Son of Eret and his crew, to intimidate the Dragon Trappers and cut Stormfly free from the ropes of the net.
He later used it in front of the trappers again to draw attention to the fact that he was still armed by igniting the blade and, after surrendering it to the trappers, tricked one of them into releasing the Zippleback gas and igniting it. Eret tried to get rid of it twice by throwing it off of the ship but Stormfly, thinking that he was playing 'fetch' flew after it and brought it back to his feet both times.
After being captured by the Dragon Thief, who unknown to him, at the time was his own mother, and her dragons, he initially tried to use the Nightmare saliva to pacify them but was unsuccessful, due to the sheer amount of dragons, surrounding him. Following this, he primed Inferno with one of the Zippleback gas canisters that he kept on his boot and sprayed it around him in the form of a circular fire-line before igniting it, succeeding in calming them before his mother interfered.
When he fought Drago Bludvist on Berk, he used the Zippleback gas as he flew past his enemy to throw him off the new alpha Bewilderbeast and, after making it safely to the ground, threw Inferno while the blade was still lit to prevent Drago from reaching his bull hook, the tool he used to control his Bewilderbeast.
- Monstrous Nightmare Saliva: By placing a small canister of Monstrous Nightmare saliva inside the hilt, Hiccup was able to coat the blade with the substance so that when ignited it produced replicated dragon fire, which convinced most - if not all - wild dragons that Hiccup was one of them. This ability could also be used to fight and intimidate humans.
- Hideous Zippleback Gas: By placing a small canister of Hideous Zippleback gas inside the hilt, Hiccup was able to release the gas through the pommel and ignite it to create an explosion, in the event that Hiccup became surrounded by dragons, to prove to large groups of dragons simultaneously that he was 'one of their own'. This ability could also be used to fight or intimidate humans. The gas, using the sword, could also work like a blowtorch or a flamethrower.
- Lighters: Inferno possessed two lighters to create sparks; each at opposite ends of the hilt as one was used to ignite the Nightmare saliva while the other was used to ignite the Hideous Zippleback gas.
- Retractable Blade: The blade of Inferno was hollow to allow pieces of the blade to slide into each other before eventually sliding into the hilt, where it is soaked with Monstrous Nightmare Saliva.
- According to 'The Art of How To Train Your Dragon 2', the sword is nicknamed Inferno.
- Inferno is one of three tools used to influence or control dragons, along with Valka's staff and Drago's bullhook
- Deleted scenes show it's possible to use the saliva of dragons other than the Monstrous Nightmare for the blade, like the Stormcutter.
- It is similar to the Lightsabers from the Star Wars franchise.
- Inferno on How to Train Your Dragons Wiki