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