ABC Tech and Games interviews two of the most senior developers on Blizzard's free-to-play Collectible Card Game (CCG), Hearthstone, Jason Chayes and Eric Dodds, about the game's worldwide mobile release, balance and their latest single-player expansion.

Hearthstone was one of the revelations of 2013: a free-to-play card game experiment that ended up becoming one of the brightest stars for Blizzard last year. It was an unqualified success, which helped push the company's efforts in the free-to-play market while opening the doors to mobile development.

Following Hearthstone's global release on iPad - which followed a soft launch that included Australia and New Zealand - game director Eric Dodds and production director Jason Chayes have been doing the rounds talking up their mobile version and the release of the game's single-player expansion, Naxxramas.

ABC: How have you dealt with all the different sized iPads and their varying levels of performance?

Jason Chayes: For us, one of our goals on all the games we release is to make it as accessible as possible and for us that's meant keeping it as wide open as we possibly could for the breadth of different iPad devices out there. It was our goal to just keep it so anybody with an iPad 2, an iPad Mini, iPad 3, going back a few generations, could still play Hearthstone and have a great experience.

We did actually cut it off at iPad 2, we didn't feel like we could bring it down to the base level, initial release of iPad and have as great as an the experience as we would have liked. But we do feel like we want to continue doing further optimisations in the future and do what we can do to improve performance over time.

ABC: You mentioned the free-to-play model and I wanted to ask you, has the process of Hearthstone as it's grown inside Blizzard created a permanent shift in the attitude or the way that Blizzard as an entire company looks at the free-to-play model?

Chayes: I can speak best to the Hearthstone stuff, but what I can say at a higher level is that there are a number of different viable business models out there. World of Warcraft uses a subscription model and we have retail releases for a number of games. For Hearthstone it's using the free-to-play model. Ultimately I think it comes down to what is best suited to the individual game, what we feel like we're trying to do with the release of the title, how we're going to be releasing content and factor that into the overall structure for the release of the game.

So I wouldn't say it's had a dramatic shift in terms of our overall strategy for our other titles and how we're planning to release them, but it is definitely something we're thinking about as it relates to our game and future free-to-play games here at Blizzard.

ABC: One of the things I wanted to ask is about the structure of tournaments and that competitive side of play of Hearthstone. We had a PAX Australia last year and there were many interesting different tournaments. I was wondering if you would ever consider coming down to Australia and running your own tournaments there?

Chayes: We're still figuring out our overall eSports strategy. We didn't really know how far eSports was going to go when we were in the early stages of beta for Hearthstone and one of the biggest surprises that's come up for us is the level of response we've got from watching various streamers putting Hearthstone onto things like Twitch and various other channels where you can watch it - which has been awesome.

We've been working over the last few months to develop a formal tournament plan and kind of start to build a relationship with some partners as to what that would look like, with a more sanctioned style tournament format. You can definitely expect to see a formal World Championship of some sort for Hearthstone and we're going to have some more announcements about that in the next several weeks. But for your initial question, we'd love to come to Australia and we'd love to be a part of the eSports scene down there and if that's something our players are looking for we'd love to come down and join you for it.

ABC: With the campaign, there are also 30 additional cards. Most of them will be free-to-play, I understand, but you'll have to pay in-game gold to unlock all of them. But you're also bringing back, or introducing, some new mechanics. How do you go about it as a developer, keeping things relatively simple and staying to that core tenet of Hearthstone of making CCGs accessible without having to lay too much on the player with every new expansion (or content) that you release?

Eric Dodds: That's a great question and we talked about that a lot and that's exactly what we are trying to hit with Naxxramas. With Naxxramas we didn't want to introduce any more keywords, like Taunt or Divine Shield or anything of the things you had to memorise. We wanted to jump into one that players already knew - Deathrattle. And then we wanted to play around more with that mechanic, so the idea is we can take a mechanic that you already know the base idea of how it works and then just play around with the ideas and explore it in ways that haven't been explored before.

So as a player you still read one of these cards, and when the card says it's a 0/2 creature Deathrattle that summons a 4/4 Nerubian I know exactly what that means, or when the card says "Deathrattle effects twice", I know exactly what that means. But they're still cool and interesting and change up the way you play the game and the way you think about decks and the way you think about the metagame. It's like having our cake and eating it too by taking [ideas] you already know and exploring them in different ways.

ABC: Have you had any feedback regarding additional traditional, fun formats that you normally see in CCGs. Magic: The Gathering has Two-Headed Giant and you have other free-for-all modes, is that something you might add in in the future?

Chayes: We definitely have gotten some of this feedback over the course of our beta. Those co-operative modes definitely are a huge amount of fun. [It's] something that teams of people have gotten excited about - the possibility of doing it with Hearthstone. One of our top goals is making sure we can maintain the readability and clarity and accessibility of the interface, so that's one of the big challenges we have... How can we build in something like that without introducing a lot of complexity or having to make things very small on the screen?

Really where we're at right now is we're in the early, early stages of thinking about stuff like that and what we'd need to do is some R&D around it to really prove that we feel like we can make a great mode that sort of stands up along the other modes we have, before we could really commit. We think the idea's cool, it's something we're thinking about but nothing we can really speak about quite yet.

ABC: For the last question, I want to ask: what has the community done that's surprised you in the way they've been building their decks and just generally how has the metagame developed that's surprised you over the course of the beta?

Dodds: That's a good question, I don't know if I have a good answer. Certainly they've made a lot of different decks and the patterns that the metagame have taken have been a little bit surprising. A specific story I have is that, early on, the Warrior was really strong and, for a number of months, that it wasn't really seeing any play at higher levels. I was just sort of baffled and then suddenly it took off and became a strong class and people sort of discovered it.

There's been this kind of fun, sense of discovery. People have been discovering things that took a path that I didn't expect. At the same time, the metagame shifts in other areas very, very quickly because of the way people stream decks [online]. All it takes is for one of the top streamers to stream a deck and suddenly it feels like all of our top players are playing that deck two days later. If you look at the metagame of a paper game, it takes weeks or months for these metagame shifts to happen. So sometimes it's been happening in ways a little more slowly than I expected and in some ways it's been happening lightning fast. It's been fascinating to watch that process.

Hearthstone: Heroes of Warcraft is available on PC and through the iTunes store for iPad and iPad Minis now.

Alex Walker is the regular gaming columnist for ABC Tech + Games. You can follow him on Twitter at @thedippaeffect.