Looking for Legendary Engrams fast? Well, we have just the technique for you but you gotta be fast before Bungie patches it on PS4 and Xbox One.
First select Earth patrol and go to the area indicated in the video below. Once you are there you may find others camping as well shooting at some cave. Aha! You have to do the same thing.
Enemies will spawn rapidly from that cave and drop lot of goodies for you to take. Once you had enough and feel like collecting all the loot from the cave, go to the portion above the cave and kill a bunch of enemies there.
Then go back to the farm spot and repeat. This method will quickly help you level the Cryptarch as well.
Check out the video below that shows this method in detail.