Dissonance

Reaching out, you strike one target's mind with a pulse of deathly energy. The target must make a Constitution saving throw or take 1d6 necrotic damage and have disadvantage on all of its following attacks against you on a failed save. On a success, it takes half damage, and does not have disadvantage on attacks.

When you reach higher levels the damage increases by another d6. At 6th level, 2d6, 13th level, 3d6, 19th level, 4d6.