Bladelust

You cause a slashing or piercing weapon you are holding to achieve a form of limited sentience that hungers for blood. For every 4 points (rounded up) of damage you inflict with the weapon on a living creature, your next attack with that weapon has a bonus of +1 to hit and to damage.

Non-Evil creatures damaged by your weapon must make a Wisdom saving throw.  On a failure, it makes its next attack roll with disadvantage.