Oogleeoog has been hanging around for as long Virginia can remember. He has told Virginia that he is a gremlin, and since Virginia doesn't know any other gremlins, she has taken Oogleeoog's word for this. As with all gremlins, at least as far as we know, Oogleeoog is at his happiest when he is causing mischief. Usually, it is at Virginia's expense, but not always.
Oogleeoog chooses to show himself only to Virginia. He considers that to be the greatest gift of friendship that a gremlin can bestow upon a human being. As such, Oogleeoog feels that Virginia should be honored to have him around.