Pokémon Trading cards, mix & match?
If you are playing casually you can mix any cards you want to as long as you have exactly 60 cards in your deck and no more than 4 of a given card (other than basic energy).

For tournaments there are a couple different formats that determine what is legal. The primary constructed formats that are played at tournaments are Standard (formerly Modified), Expanded, and Unlimited. For any of these formats if a card is legal in the format you can use copies from previous sets. The cards that are legal in each of these formats as of 4/19/16 are as follows:

Standard


XY—Kalos Starter Set
XY
XY—Flashfire
XY—Furious Fists
XY: Trainer Kit
XY01 and higher
Other sets 3 weeks after their release in the United States


Expanded


Black &amp; White
Black &amp; White—Emerging Powers
Black &amp; White—Noble Victories
Black &amp; White—Next Destinies
Black &amp; White—Dark Explorers
Black &amp; White—Dragon Vault
Black &amp; White—Dragons Exalted
Black &amp; White—Boundaries Crossed
Black &amp; White—Plasma Storm
Black &amp; White—Plasma Freeze
Black &amp; White—Plasma Blast
Black &amp; White—Legendary Treasures
BW: Trainer Kit
XY—Kalos Starter Set
XY
XY—Flashfire
XY—Furious Fists
McDonald’s Collection 2011
McDonald’s Collection 2012
McDonald’s Collection 2014
XY: Trainer Kit
Black Star Promo Cards: BW01 and higher, XY01 and higher.
Additional expansions become legal three weeks after they are released in the United States.


The card Shiftry (Next Destinies 72/99) is banned in Expanded

Unlimited


All cards from all expansions (including promo cards) are legal in Unlimited
Additional expansions become legal three weeks after they are released in the United States.