To get the quest, you have to beat the challenge mode King's fall without wiping 1. Talk to Eris Or Lakshimi (If you talk to eris you get a taken necrochasm, if you talk to lakshimi yet get a taken mythoclast) 2. Complete Crota's End or vault of glass normal depending on who you talked to, dismantle 15 gear drops from that raid 3. Complete the hard mode raid with a guaranteed necrochasm or vex mythoclast drop 4. play through the entire taken king storyline, upgrading it as you go 5. Defeat Oryx on challenge to receive "Taken Weapon core" 6. Charge core with 500 taken kills on the dreadnaught 7. turn core and weapon in to gunsmith 8. wait till reset 9. go back to gunsmith to receive taken weapon It's a little lengthy, but if say one of the perks was "after every prescision kill you became immune to damage for 3-5 seconds" it would be worth it