If this is difficult at all to implement, then forget about it, but I'm just tossing around an idea.
What if, in the trainer, players could create their own cards?
Of course we wouldn't be able to make new abilities or do anything complicated, but perhaps we could choose the cards element, type, cost, attack, hp, and ability from some drop-down boxes. Then 6 copies of that card would appear in our card list with a blank or placeholder art.
This would help those of us who are interested in coming up with new cards, because we could test out card ideas to see how powerful they are.
Just an idea,
Jallen