So, I know that with the exception of pillars/towers you can only have up to 6 of the same card in your deck. Can you add upgrade cards too? Sorry, I phrased that badly, say you have six toadfish in your deck, can you add a pufferfish (upgraded toadfish)?
Also, what kind of cards should i upgrade? Dragons, rare weapons, status/healing, creatures I just really like (like toadfish)?