History of Eidolon Ally

Overview

Eidolon Ally is a Legendary Kinetic Auto Rifle added in Season of the Witch alongside the Crota's End raid. It has a fixed roll: Arrowhead Brake, Ricochet Rounds, Rangefinder and Perpetual Motion, plus the Cursed Thrall origin trait (after a melee kill, final blows make targets explode briefly). Blueberries ranks it highly in both PvE and PvP usage for Season 22, and it is the stepping stone to the Exotic Necrochasm.

Acquisition

Defeat Crota in the final encounter of Crota's End, then start the "Bottomless Pit" quest from the Sword of Crota chest. Accepting the quest gives a white-tier auto rifle, Husk of the Pit; defeat 100 Hive with it (raid kills grant bonus progress, and the Altars of Sorrow on the Moon are a fast solo spot) to turn it into Eidolon Ally. Per Blueberries it is a fixed-roll drop found only through this questline and is not craftable; the quest continues toward Necrochasm via Essence of the Oversoul.