Hiccup applies Nightmare gel (presumably) to all the weapons the Dragon Riders, Gobber, Eret, and Valka have, including Snotlout's hammer. They fight off mysterious dragons called Silkspanners once they emerge from a cave in which they took refuge in.
Snotlout's Hammer appears during the "Wrath of Stormheart" Expansion in the game, School of Dragons. Snotlout utilizes it to fight off Grim Gnashers at Vanaheim, soldiers of Nikora Stormheart aboard The Tempest, and other opponents.
The School of Dragons iteration of Snotlout's Hammer is simply designed. It is a rounded oval-shaped stone attached with metal to a wooden handle. The handle is partially wrapped in leather ribbon for a grip.