They could also add ability cards.

Cure 1 bring 1 card that was removed from play bk to the field in place of the cure card.
Cure 2 bring 2 cards back and so on.
Provoke could draw the attention of the card being played to that card so your card
remains on the field.
Fire could reduce the targets cards numbers by 1 for the rest of the game.
They could even let you use these cards as long as they are in your hand.