You enchant the decks of playing cards, making it so that now every one of the cards in each deck has a picture of a different sexy woman on them.
Now, whenever a game is played with these cards everyone who loses he game being played will turn into a duplicate of the woman pictured on the first card they picked up in the game.
Lastly you add that no one will ever notice a problem with the cards or any of the changes that they cause.