History of Essence of Failure

Overview

This is one of the Nightmare Essence quests from Shadowkeep. It is a Eris Morn / Lectern of Enchantment quest: you buy the Essence at the Lectern in Sanctuary on the Moon, cleanse it by completing the objectives below, then return to the Lectern to turn it into gear. Reward is the Arc Logic Auto Rifle. Sources describe the Essences as costing one Phantasmal Core each, and objectives only need completing once per account (later identical Essences auto-complete those steps). The quest was part of Season 8 content; I could not confirm from the sources whether it has since been removed or vaulted, so check in game.

Walkthrough

1. Pick up the Essence of Failure at the Lectern of Enchantment.
2. Complete 50 activities on the Moon: patrols, public events and Lost Sectors.
3. Defeat 50 combatants with Auto Rifles.
4. Collect the Captive Cord in the Lunar Battlegrounds (in the building with the radio tower, per TheGamer).
5. Visit the Lectern of Enchantment in Sanctuary to create the weapon.

Rewards

Arc Logic, a Legendary Auto Rifle.