Bow of the Soul Stealer (5e Equipment)
From D&D Wiki
Weapon (longbow), very rare (requires attunement)
This enchanted, Darkwood longbow has Fey runes etched along its limbs, glowing a dark purple when the bow is drawn back. Arrows that are nocked onto the bowstring also emit a dim purple light, that leaves a very faint trail of magical energy as the arrow flies through the air.
Magic Weapon. You have a +1 bonus to attack and damage rolls made with this weapon.
Soul Stealer. After attuning to this weapon, any arrows fired from this weapon that kill a creature, consume a portion of their soul/lifeforce. Dealing a killing blow to a creature grants you half of the creature's CR rating in temporary years of life. This time is consumed before the you continue to age. In other words, If you are 30 years old and kill a CR2 creature, you gain 1 year of life but in one year your age will be 30 not 31 because you consume the creature's lifeforce that you kill before you continue to age.
This effect will not work on Undead or Elementals. If the PC ends their attunement to this weapon, they lose all the benefits they may have and continue to age as normal.