At long last Wizards is finally recognizing the brilliant Commander format for Magic: The Gathering.
Hearthstone fans will sort of get the gist: you have one Commander (hero) that dictates the cards you can take, and serves as the linchpin of your deck. I'm obviously over-simplifying it a bit, but Commander really is an apt description for it, and Wizards is taking that format and injecting standard restrictions to it with "Brawl."
The week of October 24 Wizards is embracing Brawl with in-person events, which grant you access to free Arena goodies. Basically all you have to do is link your DCI number (Duelists' Convocation International - the official way Wizards tracks players) to your Wizards account (which is separate from Arena). If everything lines up, you signed up for email promotions and your store uploaded the info correctly, you'll get one copy of the three below cards for free, on top of styles for each of them. Those codes should go out on October 31, the week after the event, and you don't need Arena to receive them.
That's it! You go to the physical event and you get digital cards. It's similar to the promos Wizards has already been running (like getting free limited play codes), and for now, it seems like this is the only way to get the styles for each Brawl card.
Arena Codes at Magic Weekend: 2 Questions You'll Probably Get [Wizards of the Coast]