Can you play four of each in a deck? Sure. I don't see why not. The rule is that you can't play more than four of any card with the same name. So you couldn't play four of each Charizard EX. (I think there are like three.) However, very rarely do people play four of any given EX because at two prizes a piece, three will be the most you will ever need, especially if you have other options for attackers in your deck.