Aerena - Clash of Champions had Steam trading card support added on May 1, 2014. There are 8 cards in the series. Because Aerena - Clash of Champions was a Free to Play Game, cards were earned by purchasing in-game content (approximately $9 USD per card drop).
AERENA - Masters Edition is the updated version of the game. Clash of Champions has been delisted on Steam, although its trading cards and items are still available in the Steam Community Market.