Destiny would like you to think it's a game about saving various planets from impending alien doom. Its millions of players will tell you, however, that it's actually about the endless quest for Gjallarhorn, an exotic rocket launcher that far outstrips anything else in the game in terms of power. Gjallarhorn has a perk called "wolfpack rounds," which are homing missiles that burst out of the rocket upon its already-devastating initial impact and continue to track targets, which is exactly as useful as it sounds.
Basically, if you want to end the game's sometimes interminable boss fights as quickly as possible, you're going to want a Gjallarhorn. The only problem is, it's very hard to find for most players, with a low chance of dropping at the end of high-level activities.
You have 48 hours to earn 17 strange coins
Well, good news: now you can just buy one from a dude with weird tentacles for a face. Xûr, the exotic item vendor who shows up in the Tower for 48 hours at this time every week, is selling Gjallarhorn for the first time since the week after Destiny went on sale — a time when almost no one had any idea of the weapon's essential nature. You'll need 17 Strange Coins to pick it up; these can be earned through activities like the weekly heroic strike, the Prison of Elders, and so on. You have until 5AM ET on Sunday morning to get them.
I have personally played Destiny for something like 160 hours without ever coming across a Gjallarhorn, so I'm buying three. Even if Bungie is nerfing the wolfpack rounds in an update ahead of the next major expansion, The Taken King.