Enfeebling Hand

You touch a creature and afflict them with spores that sap their strength away. Make a melee spell attack against a target. On a hit, the target takes 1d8 necrotic damage. The first time the creature deals damage after making an attack roll, roll 1d8. Subtract the number rolled from the damage the target would have dealt. The effect dissipates at the start of your next turn. On a critical hit both the damage dealt and damage reduced are doubled. 

The spells damage and the spells damage reduction increases by 1d8 at 5th level (2d8), 11th level (3d8), and 17th level (4d8).