Deathmark Spear

Weapon (spear), rare (requires attunement)

This item has a grotesquely-carved ebony shaft mounted with a cruel-looking spearhead fashioned from a wyvern tooth. You gain a +1 bonus to attack and damage rolls made with this magic weapon.

In addition, when you attack a creature it is magically marked. Your subsequent attacks on the marked target have advantage and do an additional 1d6 piercing damage. If you kill a creature marked by the spear, you gain 2d6 temporary hit points. Only one creature can be marked by the spear at a time, with the mark leaving previous creatures when you attack a new target.