How to get Destiny Husk Of The Pit Rifle, Eidolon Ally Legendary Auto Rifle and Necrochasm Exotic Auto Rifle

A Common Auto Rifle in Destiny which is described as "Dessicated and nigh-inoperable this Hive artifact still manages to send shivers up your spine when fired," can be found in the Blade of Crota on Earth and the Moon after the Destiny Patch 1.1.0.2. Guardians can get this weapon while either being on Patrol or while re-running through the Fist of Crota mission.

Husk of the Pit automatically adds to the Guardian's inventory with a notification on right-side of the screen. The rifle will appear as the random reward after killing the Knight. No active Black Wax Idol, combination of items or status is required to get the Husk of the Pit.

How to get Destiny Husk Of The Pit Rifle

1. Begin with Fist of Crota story mission on Earth
2. Complete or get past the first stage with Omnigul
3. Disturb the Hive ritual
4. Kill the "Blade of Crota"

Guardians need to re-do the above steps if they are unable to get Husk Of The Pit Rifle.

How to get Destiny Eidolon Ally Upgrade for Husk Of The Pit Rifle

The Eidolon Ally upgrade for Husk Of The Pit Rifle is described to the Guardians as "We thought it was inanimate but it has grown...changed. Ghost refuses to analyze it further but I secretly believe it has become my friend." Eidolon Ally is the second evolution of Husk of the Pit rifle, it turns the Rifle into a Legendary Auto Rifle. 

1. To get the Eidolon Ally Upgrade for Husk Of The Pit Rifle, Guardians need to purchase one Embalming Orb from Eris Morn for 10 Black Wax Idols with level 3 reputation with Eris. Getting the Embalming Orb will unlock Cannibalism perk.
2. After unlocking Cannibalism perk, destroy 500 Hive enemies (re-do The Dark Beyond, Chamber of Knight, Crota's End Raid etc. for Thralls swarms) to turn Husk Of The Pit Rifle into Eidolon Ally Legendary Auto Rifle.

How to get Destiny Necrochasm Upgrade for Eidolon Ally Legendary Auto Rifle

Necrochasm is the third evolution of Husk Of The Pit Rifle described as "Eternity is very close. Can you feel yourself slipping?" It is an Exotic Auto Rifle which appears in The Dark Below DLC after completing certain tasks. Necrochasm is a very-low Impact, very-high ROF with highest Stability, the only downside is the smaller Magazine.

1. Guardians need to complete The Burgeoning Hunger perk on Crux of Crota by killing the The Dark Below Raid boss on hard mode.
2. Then an unknown number of Hive kills to upgrade Eidolon Ally Legendary Auto Rifle into Necrochasm Exotic Auto Rifle.

While none of the Guardians have the Necrochasm Exotic Auto Rifle, one of its perks, The Cursebringer perk's precision killing has become famous which triggers a Cursed Thrall explosion.