Vampiric Kings Blade (5e Equipment)
From D&D Wiki
Weapon (shortsword), Rare (requires attunement by a creature with the Vampire Curse)
Each time the sword becomes bound to a new master, the shape of it changes slightly. This sword grants a +2 to all hit and damage rolls made in dim and dark light. This weapon deals 1d6 + your Dexterity mod and an extra 1d6 in dim or dark light.
Blade of the Old King The blade is invisible and covered in black mist in sunlight and only shows its true form in dim and dark light.
Blood Sucker Recover half damage dealt with this weapon as hit points.