The cloaked ghost ones looked decent enough but they have an error, and a B unit is different than a slug. A B Unit is a powered loco with prime mover and traction motors, but with no cab. It must be MU'ed to other locos to work. Sometimes they have hostling controls which give them a basic movement capability. I one case, a B Unit was given remote control and a control stand on the conductors side so it could work as a mine switcher. A slug just has traction motors so it can give a loco more pulling power. Sometimes these have cabs so they can lead, or remote control so they can give non-RC locos RC capabilities.