Soul Eater (5e Equipment)
From D&D Wiki
Weapon (evolving weapon), rare (requires attunement)
This unique weapon hungers for souls and is a potentially very powerful weapon. This blade is made of a foreign metal that is dark as night and swirls like that of a galaxy to the chosen wielder, but to all other players and npc's this blade seems to be a dull black blade that is ice cold to the touch.
When this blade kills a creature(undead and constructs do not count) it consumes its soul gaining +2 so its soul count, when first gained this sword has 2d6 - 1 souls.
The blade has a +1 bonus to attack and damage rolls and starts as a shortsword. Upon consuming 10 souls it will grow into a longsword, and upon consuming 20 souls it grow into a greatsword.
Once the blade grows into greatsword form, each additional 10 souls it consumes it deals an additional 1d6 slashing damage. (Weapon's max soul capacity is 60, so at 60 souls this weapon deals an additional 4d6 slashing damage)
Curse: If the wielder of this blade dies, the weapon will consume their soul. Only the wish spell can bring a person back to life when they die this way. This curse can only be removed by that of a wish spell. The remove curse spell only temporary halts this effect for 24 hours.