Bloodthirsty Strike

From the Blood Fury Tattoo:

Bloodthirsty Strikes. The tattoo has 10 charges, and it regains all expended charges daily at dawn. While this tattoo is on your skin, you gain the following benefits:

• When you hit a creature with a weapon attack, you can expend a charge to deal an extra 4d6 necrotic damage to the target, and you regain a number of hit points equal to the necrotic damage dealt.
• When a creature you can see damages you, you can expend a charge and use your reaction to make a melee attack against that creature, with advantage on your attack roll.