A sword of deepest corruption and conviction, it cannot be the demon's blade that drove a city to madness. It cannot have been reborn in arcane energies somehow fey and fiend and undead intertwined. And it cannot have inspired in the name of one who desecrated the temples of the gods. One wonders what this sword cannot be next, in the hands of a reckless adventurer, if they are not careful.
Material: Planar Alloy
Unique Attributes: Reborn
Weapon (greatsword), legendary (requires attunement by a non-good alignment).
When attuned to Certainty, the wielder gains a +1 bonus to attack and damage rolls made with it. Whenever Certainty damages a living creature, that creature must roll a Constitution saving throw (DC 12). On a failed save, Certainty 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.
The bonus to attack and damage rolls increases to a +2. Grants the wielder advantage on Charisma (Intimidation) checks when unsheathed.
The bonus to attack and damage rolls increases to a +3. If Certainty devours enough strength 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.
It is said that after a terrible demon was felled outside the gates of Vor Rukoth, his broken blade was mounted as a trophy above the slayer's fireplace. When news of his victory reached the master smith Tavus, the paragon journeyed out of the dwarven kingdoms to the surface, to Nerath, to the slayer's home in Vor Rukoth. Tavus traded one of his masterwork swords for the broken trophy, and returned to his forge. Yet no matter what Tavus tried, he could not reforge the sword.
Sending for aid from the Spire, the first enchanter himself answered Tavus' call. The task of reforging the sword took no less than ten years, and required materials and artifacts not only from the abyss, but also from the feywild, and from beyond the shadow veil. Throughout this time, the broken blade corrupted both Tavus and the first enchanter. On the day their work was finished, and Certainty reborn, Tavus lost the favor of Moradin, and the first enchanter struck him down with his last masterpiece.