This is a self working, visual magic effect which is a treat to the eyes of even a magician.
Magician shows a packet of regular size cards which has Ace of Spades, King of Spades, Queen of Spades, Jack of Spades and Ten of Spades respectively in a row. He says, “These cards are magic cards, let me show you one of their magical powers.”
The magician says a few magic words and all of a sudden, the cards change into different sizes. One card, i.e. Ace of Spades changes into a jumbo size and the other cards become progressively smaller right in front of the audience.