Fishlegs' Sword has the appearance of any common sword. It is long, becoming thicker at its top. Its handle is brown, probably made of leather.
When Meatlug spits out a lot of lava in the smithy, Gobber decides to use it and makes a sword out of it. Later, he shows it to the Dragon Riders, much to their surprise. Astrid comments how it is lighter, but it would be useless in a battle. Gobber then demostrates otherwise, cutting Snotlout's sword in two.
The sword appears again at the end of the episode, when Gobber gives it to Fishlegs, thanking him for the job he did at the smithy.
Dagur the Deranged acquired Fishlegs' Gronckle Iron Sword during one of his many attacks on the Dragon Riders, before he made an alliance with them. In "In Plain Sight", he brings out the sword, as well as assorted other items to tempt Ansson to trade for a Dragon Eye lens he had taken from Dagur as children. Ansson is not interested in the sword or any other item, though Fishlegs takes his sword back.