Amarth Nathron, the Weaverender

The fell blade of Amarth Nathron has a baleful and violent history. Forged by the elven swordsmiths of Ygtoryn in the Greywood, this artifact was used first to reopen and maintain a great rift between the material plane to the Evenglade, the elves' ancestral home and the source of much of their magic. The elves bound the spirit of the hamadryad Balanaea to the blade and planted it in the keyarch of the rift: a swirled knot in the great Bloodoak at the heart of Ygtoryn.

The binding of such a being to an object of metal is tantamount to sacrilege to the Fey, and when they discovered what their elvish kin had done, the typically-inimicable Courts of Oak and Holly vowed together to punish the slight. With the help of an ancient coven of hagmothers, they placed a curse on the blade, poisoning the imprisoned soul of Balanaea and draining her of her last shreds of vitality and turning her aspect dark and grey. The blade itself turned from gleaming silver to matte black, and the bloodoak hilt grew gnarled and grey. As this transformation took hold, so too did the nature of the gate change: rather than opening into the perpetual gloaming of the Evenglade, it became a portal to the fog-choked midnight of the Nightshade, a dark echo of the material world populated by undying souls and terrifying monstrosities. The hordes of the night swarmed from the gate, and wreaked destruction upon the elves of Ygtoryn. Eventually, after much bloodshed, the flood of undead horrors was driven back to its source at the gate,  but the elves' endurance was flagging. In a desperate bid, a young elven warrior named Svanhildr grasped the twisted hilt of Amarth Nathron and yanked it from the Bloodoak. The gate closed suddenly, a great vortex of wind and negative energy drawing everything near it into the darkness of the Nightshade. In a moment, the battle was over, and the world fell silent. Only the sword remained, a talisman of the elves' hubris and cruelty.

Those who remained agreed that the blade should be shattered, and the fragments dispersed. One they sent to the west, across the Greyspine into the land of Oster, where giants were said to rule vast kingdoms; another they carried far past the Southlands, to the plains and wastes beyond; the third was cast into the dark, unknown depths of the Scura to the northeast, and the bloodoak hilt they buried, chained beneath the frigid, subterranean waters of the Neve.

Elfsbane. You have a +3 bonus to attack and damage rolls made with this magic weapon. It deals an additional 2d8 slashing damage to elves and half-elves. While attuned it, you have resistance to necrotic damage, and can see normally in magical and non-magical darkness out to a range of 120 feet. 

Dismal Shroud. A creature attuned to Amarth Nathron becomes drained of all color and vigor: over the course of the first 24 hours of attunement, the wielder's appearance, and all belongings worn and carried by it change color to shades of grey, and they gain the following flaw: "I disdain the trappings of life; food, drink, music- all are a nuisance to me." Additionally, the area within 30 feet of the wielder cannot be brighter than dimly lit, and all color within that radius is muted. Creatures other than the wielder have disadvantage on death saving throws while in that area. The blade is eager to drag all near it into the dismal realm of the Nightshade.

Weaverender. The sword has seven charges, and regains 1d6+1 charges every day at midnight. When a creature attuned to Amarth Nathron hits with a melee weapon attack with this weapon, they can expend one charge to force the target of the attack to make a DC 18 Charisma saving throw. On a failure, the target is banished to a corresponding location in the Nightshade, where they are frightened. While frightened in this way, the target is incapacitated and their movement speed is reduced to 0. At the end of each of the target's turns, they can repeat the saving throw, ending the effect and returning to the spot they left on a success, taking 3d10 force damage. An undead creature attuned to the sword can use an action to spend 7 charges and plant the blade in the ground, creating a syphon of negative energy in a 30 foot radius, 30-foot tall cylinder. All creatures in that area must make a DC 18 Charisma saving throw, or be transported to a corresponding location in the Nightshade and take 5d8 necrotic damage. On a successful save, a creature takes half of the damage and is not transported. The wielder automatically fails the saving throw, but takes no damage. The area affected by the syphon becomes polluted with magical darkness. All areas of light created by spells of seventh level or lower that overlap that darkness are dispelled.

Sentience. Amarth Nathron is a sentient chaotic evil weapon with an Intelligence of 14, a Wisdom of 6, and a Charisma of 18. It has blindsight out to a range of 5 feet. While wielded by a creature attuned to it, the weapon can see and hear through its wielder's senses. The weapon communicates telepathically with its wielder, and can speak, read, and understand Elvish and Sylvan.

Personality. The shattered spirit of Balanea still lingers in the blade, but her containment and division has rendered her mad. She whispers vengeful gibberish to her wielder in Sylvan, often listing the names of the long-forgotten elves who bound her to the sword. When her wielder encounters a humanoid of elven ancestry, she urges violent and destructive action against them. If her hatred is ignored, a conflict arises between the blade and its wielder.

Destroying the Blade. Once reforged, the blade will not allow itself to be broken again. It can only be destroyed once every living descendant of its original crafters has been slain, at which point the spirit trapped within it is put to rest. Then, the blade becomes no harder to destroy than a normal longsword. 

 

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Resistance: Necrotic, Damage, Banishment, Combat, Sentient, Versatile, Sap