Brain Rot

You cause a fungus to form in the brain of a target you can see within 60 ft. causing them to make a CON saving throw against your spell save DC. On a failed save the target takes 1D8 necrotic damage and has disadvantage on it's next attack roll.  On a succesfull save take half the damage and this spell has no further effect. Doesn't work against enemies that don't have a brain.