Craven Edge

 is a sentient, thick, onyx, two-handed greatsword once wielded by Sylas Briarwood and then by Grog Strongjaw before being thrown into the pocket dimension of the Dread Emperor. Imbued with dark arcane power, Craven Edge drains strength from the foes it strikes, absorbing their blood into its blade. It may even consume the soul of its wielder, as it did with Grog. As an NPC, Craven Edge is portrayed by Matthew Mercer.

While severing Craven Edge's connection to Grog's soul, Pike Trickfoot saw a vision of a nameless man striving for power and wealth, then striking a deal with a dark entity. The man didn't fully understand the deal he had made, and Pike glimpsed the dark entity punishing him for an unknown action he had made. The dark entity bound the man's soul to the blade now known as Craven Edge, cursing his soul in the process, condemning him to eternal gluttony and an insatiable desire for strength and blood.

Banishment
After Pike severed Craven Edge's connection to Grog with a Greater Restoration spell, Keyleth banished the evil sword to the Dread Emperor's realm using Plane Shift. Due to the conflicting statements about the Dread Emperor's realm, it is unclear if Craven Edge is now in the Astral Plane, in a pocket dimension, or somewhere else altogether.

Features

 * Dark Aura:  Grants the wielder advantage on Charisma (Intimidation) checks when unsheathed.
 * Devour the Weak:  Whenever Craven Edge damages a living creature, that creature must roll a Constitution saving throw (DC 12).  On a failed save, Craven Edge drains one point from the creature's Strength score and transfers it to the wielder (increasing to a maximum of 25 Strength) until the next short rest.  Creatures brought to 0 Strength by this feature are slain.
 * Gluttonous Evolution:  If Craven Edge devours enough strength from Devour the Weak to bring the wielder to 25 Strength, then the blade shifts form into a larger, jagged blade that seeps shadow.  Until the wielder's next short rest, all attacks with this sword deal an additional 2d6 necrotic damage.   After the short rest, the attuned creature must make a Constitution saving throw (DC 16) or have the now-hungry weapon, energy spent, devour the wielder's soul, causing instant death.

Quotations

 * "You... are you my new wielder?  [...]  Leave me until one worthy lifts this blade.  I am useless left here; I seek the thrill of battle—I am hungry."
 * "Do you enjoy drinking the strength of your foes, watching them beaten before you, and have that very power become your own?"
 * "Do you wish the shadows to encase your form and grant you resilience in anger, forcing those to kneel before you in fear?"
 * "No...  Keep the tears flowing."

Trivia

 * Craven Edge is an anagram for "Vecna Greed".