The Arm of Nerull
Weapon (longsword), legendary (requires attunement)
A longsword made of an unknown dull gray metal with dull runes etched into the fuller on one side of the blade. A pair of green precious stones adorn either side of the thick silver cross-guard. The hilt is wrapped in dark leather.
The runes on the blade are in Soloise and reads Arm of Nerull. The dark leather that wraps the hilt is human flesh.
Even if you are not attuned to The Arm of Nerull it is still considered a magical weapon when you wield it. If you are attuned to the Arm of Nerull, you gain resistance to necrotic damage whiule The Arm of Nerull is is carried and deal an extra 1d6 necrotic damage when you hit with the weapon.
Embrace of Nerull. You can use an action to have Arm of Nerull to create a 60-foot cone of negative energy that deals 7d6 necrotic damage to all creatures within its area and has their maximum hit points reduced by the same amount. A successful DC 14 Constitution save reduced the damage and subsequent reduction of maximum hit points in half. Once used, this ability cannot be used until the next midnight.
The command word for the embrace of Nerull is a prayer to Nerull “Nerull welcomed you into his embrace.”
Exhausting Damage. Any creature that suffers necrotic damage that originated from The Arm of Nerull, whether it is from being hit by the weapon or from Embrace of Nerull, must make a DC 14 Constitution save. Failure means that they suffer a 1 level of exhaustion. If the save failed by 5 or more, they suffer 2 levels of exhaustion and fall unconscious for 1 hour.