I think it wold be cool to expand the crafting aspect of this game. After each battle you could gain different materials to help you craft cards with like many other games do. I like the idea of crafting but all the cards that you can craft are outdated, old or simply not worth crafting.
I like this game a lot its very addicting I only recommend that energy increases s you lvl up and maybe try to equal out the ranks in arena. Aside from these minor suggestions great job:)
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Reviewing the crafting system is on our list :) Thanks for your ideas!