It's a deck of magic cards!
This special deck of cards is created with the Hi-Visibility 52-on-1 deck. It's gimmicked. The deck does all the work.

Effect: 
The spectator freely names any card in the deck.

The performer announces the named card was a prediction that can be proven because it is the "top card of the deck in the closed card box." When the performer removes the deck from the box, it is revealed that EVERY CARD is printed on the top card of the deck.

Yes! It was a joke, but also a set-up for the big finish:
The performer spreads through the deck to show that every card has the same back design, BUT, when the named card is removed, it is shown to be the only card in the deck which has an 'X' drawn on the back of the card, RIGHT ON THE MINIATURE IMAGE of the selected card!

This is the Happy-Sad-Happy plot: First the audience is happy because they expect a good trick. Then they're sad because it was just a joke. Then they're happy because it turned out to be a great trick!