Got my first Gjallarhorn from a legendary engram in the Loot Cave, didn't even know what it was and the only reason I didn't shard it was because it looked cool, but it still stayed in my vault for months until I decided to level it up. Hard Light which I also got that same night from a legendary from leveling up the cryptarch off the engram that yielded Gjallarhorn got a lot more use. My friend that I had been playing with was pissed, all he got was some warlock armor called Heart of Praxic Fire. Did I earn either of those weapons? Hell no, any fool can shoot into a cave. The only weapons anyone has ever earned are the exotic bounties and the raid weapons such as Vex and Black Hammer. I had to kill Aetheon 23 times and Crota over 30 times.