Transformer

Let your spectator remove a card from the deck, and hold it aside.
You then produce an envelope containing a playing card- the card you think will match your spectator's.
When you show your card- it does not match.

BUT WAIT!
Give the side of the card a flip- and it starts to TRANSFORM!
Just like the Transformer machines!
This crazy card not only turns itself inside out and back to front, but at the same time changes from YOUR card into YOUR SPECTATOR'S CARD!

And it's easy!
If you can flip the flap on a card, you can do the trick!