NB Southern Railway’s slug NBSR 001 was rebuilt from an ex CN slug.
The slug has no diesel engine, but does have electric traction motors. It draws its power from the paired engine, the “mother”, which has extra power available at low speeds. The slug provides extra traction and braking power at low speeds. NB Southern’s equipment cuts power to the slug above 25 MPH as there isn’t enough spare power from the mother’s generator/alternator at higher speeds. More information on slugs
See also NBSR 008, their first slug.