This is an absolutely great gag style effect which uses just an ordinary looking beer mat on the table with your drink on top.

A card is selected, remembered and returned to the deck. You claim you will make their card appear under the glass. Now follows some hilarious bits of business in which you repeatedly fail to make the card appear under the glass. In desperation you lift the glass up and the beer mat visibly changes into a jumbo duplicate of their card. A hilarious gag trick, which is not without serious applications.