To everyone who doesn't have it, go! Buy Three of Coins from Xur NOW! Then, go to the garden spire mission on Mars, you know the one! Play to the end, but don't forget to pop Three of Coins right before you kill the boss! Scan the device only the first time! After you kill the boss, return to orbit without scanning the device! Return to the mission, you will have to kill adds over again, but you won't lack ammo, scan only the first time, then orbit. Rinse and repeat! You'll get exotic engrams in no time, doesn't matter the difficulty! :D