This trophy is cumulative and you will easily obtain this through running the dungeons, trying to conserve your health. There are plenty of Shadows and many of them have an accessible weakness until you get to the fourth Palace. Be sure to try any and all attacks available to you until you uncover it to Down them. If you negotiate a new Persona, the stats will be revealed permanently on minor Shadows (you might find that specific mini/mid-bosses will have differing stats from their normal forms).