Gjallarhorn is an Exotic Rocket Launcher with exceptional Velocity and great talents. In addition to Tracking rockets, a detonated rocket splits into "tracking cluster missiles" – Wolfpack Rounds. These rounds deal enough damage to kill an undamaged secondary target in Crucible.
Like Dragon's Breath, Gjallarhorn was crafted in the labs of Feizel Crux and Victor Lomar:
"If there is beauty in destruction, why not also in its delivery?" - Feizel Crux
The Gjallarhorn shoulder-mounted rocket system was forged from the armor of Guardians who fell at the Twilight Gap. Gifted to the survivors of that terrible battle, the Gjallarhorn is seen as a symbol of honor and survival.
The Battle of Twilight Gap was a major siege against The City, led by the Fallen's House of Devils and felt the "combined might of the Fallen Houses". The defense was led by Lord Saladin Forge, and further commanded by his protégés Commander Zavala and Lord Shaxx.
"Max Gjallarhorn Only"
Gjallarhorn is a very potent weapon against PVE bosses. When Crota's End was released, the community agreed Gjallarhorn was almost a required weapon for defeating Crota. This was because the extra damage from Wolfpack Rounds and how they prevented Crota's shield from recharging.
As such, ownership of a "max Gjallarhorn" (331 ATK) became a frequent sight in "Looking for Group" posts.