Nine Lives Stealer

(Requires attunement)
You have +2 bonus. The sword has 1d8+1 charges
If you score a critical hit against a creature that
has fewer than 100 hit points, it must succeed on
a DC 15 Constitution saving throw or be slain instantly as the sword tears its life force from its
body (a construct or an undead is immune). The
sword loses 1 charge if the creature is slain. When
the sword has no charges remaining, it loses this property.