You've made a great game that's got me playing way past the end of the demo because its just that *fun*.
Which means I, being a wannabe game developer, am now going to share my opinions unprompted. Feel free to ignore everything I say, its probably for the best, but maybe one or two suggestions are actually decent
Okay so first off, major continuity issue / mechanic suggestion! Buying cards. We've got the ability to sell cards, that's good, however its described as hacking to transfer card ownership. Which, after opening countless packs, got me wondering: Why can't we buy cards? Surely there'd be no reason why we couldn't find someone else selling cards and purchase them, to add those cards to our account? I understand that balancing-wise it'd be a bit of an issue, but maybe the person running the card-selling service is incredibly greedy and it costs 10x the sell price of a card to buy it.
Second, username change! This one's just a personal thing, but making players pick their own username instead of assigning them one of the random ones might be fun
The control bar; It doesn't stick around. Even moving my mouse to the top of the screen doesn't bring it back, so if I maximize a battles window I can't un-fullscreen it to check my other stuff without first fully exiting the game. Feels a bit weird, honestly.
actually that's about it. You made a really solid game! Already wishlisted it on steam, looking forward to it!