Standard term in trading-card games — Yu-Gi-Oh! (《游戏王》), Magic: The Gathering (《万智牌》), Hearthstone (《炉石传说》). The classifier is 副 (fù), the same as for an ordinary deck of playing cards.
memory
牌 ('card / tile') + 组 ('group') — literally 'card group'. Compare 牌堆 (páiduī, 'card pile' = the deck you draw from) and 手牌 (shǒupái, 'hand cards').
