Hint: Poseur Co-Op
When playing with a character from the Hero side, a second player can controll that person, but they cannot use any weapons or cars.
Hint: Choose Your Morals
Shadow's dark-light leaning is determined by his ability to hurt or heal enemies (note this is not the IGN board phenomenon). You definitely need the Heal Gun to carry this through. When attacking soldiers (stages include Westopolis and Death Ruins), simply heal them right before they die and you will gain massive evil points for simply attacking them.
For good points, all you need to do is heal them 9without attacking). For each action of healing, Shadow gains one hero point, whether or not the target is wounded.