Mary-Jane is the friendly ghost kitten from Pups and the Haunted Clubhouse.
Mary-Jane is called her name because when she was in her body, she had two owners: twins named Mary and Jane and they compromised their names on her. But her paws also make it look like she's wearing Mary-Jane shoes.
After she became a ghost, she became the Ghost of Pet Past. She has the ability to take pets to the past and try to change a past that doesn't deserve what past it has.
We never see Mary-Jane when she was in her body. As a ghost, she is white but some of her brown fur is seen on her paws that shows her Mary-Jane shoe look-alike-ness (or some way of saying it, but I think you get it...)