Destiny Eris Morn Bounty GATHER THEIR FURY
You need to buy it from Xur for 1 Strange Coin. Eris Morn will then give you quest steps that you need to complete. http://youtu.be/dbW87zUagZ8
Start the mission “The Wakening” on the moon and play it about halfway through. You will come to a room that is filled with Cursed Thralls. “Gather Their Fury” you to collect Seething Mist from them without dying. If you don’t pick them up you are allowed to die though. Which makes this a lot easier.
Pick one from the group and shoot the Thrall a little, then 1 hit melee kill it. You will die by the chain reaction and respawn right before this section and the Seething Mist will still be there. Repeat this 4 more times and pick the Mist up once you have 5 laying around.