I just realised another weakness of Sam. He might be able to let things go through him and vice versa, but a shadow always needs a point of origin. This means that he cant just walk through a 3 meter thick wall, as he would be completely in it. This also means that, in his normal form, you could crush him by making a big solid block fall on top of him. However, in his shadow form, he could just reshape into a flat shadow and survive it.