Inferno

The Inferno also known as the Dragon Blade, is Hiccup's main weapon in the second film.

Lore
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. 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.

In How to Train Your Dragon 2 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.