An Old Man's Cards

Whenever this set is in use, a creature that can only be described as a familiar is made visible. The creature is a light-skinned human man with a five-o'clock shadow in his mid-forties.

Only the owner is able to see and hear him as he occasionally gives "advice". 

He allows the user to see through their opponents' cards, would switch out one card for another still in the deck, and even suggests when to push your luck. All of these are done at the creature's discretion. 

Surprisingly, a game of solitaire is how most people talk to him. Probably because talking to an invisible man with other people nearby is frowned upon.