Weakening Blade

As part of the action used to cast this spell, you must make a melee attack against one creature within the spell's range, otherwise the spell fails.  On a hit, the target suffers the attack's normal effects, and it must make a Constitution saving throw.  Unless the saving throw is successful, the target takes 1d6 necrotic damage, and the first time it makes a Strength, Dexterity, or Constitution saving throw before the end of your next turn, it must roll a d4 and subtract the number rolled from the save.

This spell’s damage increases by 1d6 when you reach certain levels: 5th level (2d6), 11th level (3d6), and 17th level (4d6).