Wow, that's quite the play through! What was challenging about it, the enemy card levels were getting too high and you'd keep running out of cards?
No, I meant the challenge was getting rid of all cards. There legendary card that beats all others except itself but it actually beats itself if it has higher level. So I found I had to (after being very ahead in the game and upgrading this card to a quite high level) let the game catch up with me again and for there to be a card that beats mine :)