Inferno

Inferno is the name of Hiccup's new flaming sword he uses in How To Train Your Dragon 2.

How It Works
This awsome weapon Hiccup designed seems to be powered by the saliva/sweat of a Monstrous Nightmare, which keeps the sword alive with fire. Hiccup also carries small pouches of Hideous Zippleback gas that burst on impact and create a fireline that can be used to the wielder's advantage.