Rover is a very large, black, six-eyed dog monster. Its eyes are ruby-colored and seem to have a glow. It has very large fangs and four toes per paw. Its fur is very shaggy and roughed up, especially on the outer part, whereas the inner part of its body presents less hair and shows clearly its muscles. It has no visible ears or a nose.
After the Monster Association incident Rover shrinks to the size of a puppy sometimes  it is the size of a big dpg The reason for its shrinking is unclear