Blackwood's Craving Edge

Whenever you make a successful melee attack whilst this spell is active, the target must make a Constitution saving throw, on a failed save the spell drains a portion of their strength and transfers it you, on a success nothing happens. For a every failed save the target loses 1 point from their strength score and you gain 1 point to yours (to a maximum of +5 to your strength score) 

When this spell ends you lose the bonus to your strength score you have gained and must make a Constitution saving throw, on a failed save you gain 1 point of exhaustion