Hearthstone is the latest success story for a studio that already had its share of them, but something about the free-to-play digital card game for PC and iPad (with iPhone and Android releases on the way) seems special.

Usually, Blizzard works on large, expensive, and epic games like World of Warcraft and Diablo III. But Hearthstone is making a huge impact of its own thanks to charm and engaging gameplay. It released its newest expansion, Goblins vs. Gnomes, earlier this month. It added 143 new cards, vastly changing the status quo.

To discuss the new expansion and the general success of Hearthstone, we talked to two of the game’s designers from Blizzard, Ben Brode and Mike Donais.

GamesBeat: How did the Goblins vs. Gnomes idea come about?

Ben Brode: Well, we love goblins and gnomes. Eric Dodds, the game director for Hearthstone, was actually the first designer on World of Warcraft. He ended up working on trade skills. He designed the engineering trade skill. He created goblin and gnome engineering and all those crazy items.

We were sitting around in the meeting room all writing ideas on the whiteboard, just pitching ideas back and forth, coming up with cool stuff, and somebody pitched goblins vs. gnomes. I wrote it on the whiteboard and looked over at Dodds, and I could just see his face light up. I said, we can stop now. We’re definitely making this expansion.

Annoy-o-TronThere was a lot of passion and excitement, both for being able to explore cards like the Goblin Shredder and other fun mechanical minions, and also just expanding the IP a bit. We got to make a bunch of new mechs, like the Snowchugger and the Annoy-o-Tron. We could explore deeper than we had with any previous content in Hearthstone.

GamesBeat: Considering the close proximity between this and the World of Warcraft: Warlords of Draenor launch, was there any pressure to do a Warlords-themed expansion?

Brode: In general, we feel pretty empowered. Blizzard is an awesome place to work, and one of the themes, I feel like, working on the Hearthstone team, is that we get to flex our creative muscles and try cool stuff. The whole company is excited about the team. I wouldn’t say that we get pressured into doing anything, really. We’re superexcited about Warlords, so we would be excited to explore the content and themes like that at some point, but I don’t feel pressure. Mostly I feel excitement from around the company.

Mike Donais: We just want to do what’s fun. We’re encouraged to do what’s fun. They trust us completely.

GamesBeat: Is it scary to release that many new cards at once, not knowing exactly what effect it might have once the masses get ahold of them?

Donais: I’d say more exciting than scary. Having all those new shifts to the meta is great. So many different new decks. You’re so excited. I wanna do this! I wanna do this! Lots of cool new stuff. Not too scary. Maybe early on, but as we progressed through the design, we got a handle on exactly how everything is going to go. There’s a lot of stuff we don’t know exactly how players are going to use, but we hope that it’ll end up all right.

GamesBeat: Walk me through the life of a card. What comes first? Do you pick a character from the lore and try to think of a way that could be a card, or do you usually come up with a mechanic and then find a character for that?

Brode: We do it both ways, actually. We often will start with a list of things we definitely want to have in a set called Goblins Vs. Gnomes. We want a Goblin Shredder. We want some gnomish engineers and goblin engineers. We want a Madder Bomber. We think about how we could translate these ideas into cards.

But also we think about what are some cool mechanics for a set about goblins vs. gnomes? Let’s try making “mech” a thing. How do we design some cards that interact with mechanical minions? Spare Parts — that’s a cool idea. Let’s make some cards that interact with spare parts. How do we do that? So we come at it from both directions.

Kezan MysticWe also think about what tools we want to give players to be able to counter things, get things a bit under control. If Death Rattle becomes a huge thing, we want to have some answers to Death Rattle to put in your deck if you’re tired of getting your butt kicked by that particular thing.

GamesBeat: It does almost seem like a response to all the Death Rattles added in the Naxxramas expansion.

Brode: Really, we just want tools for every possible strategy. If you’re frustrated by secrets you could put in the Kezan Mystic. If you’re frustrated by beasts you can put in Hemet Nesingwary . Just adding a wide variety of tools is important.

GamesBeat: The nice thing about having a lot of cards now, there seems to be a counter to almost anything. It just comes down to what you’re going to make room for.

Brode: Right. Anticipating what kinds of decks are going to be popular at the rank you’re playing at is an important part of figuring out which card to put in your decks.

GamesBeat: It seems like for this expansion, you have things like the Spare Parts, cards that materialize depending on certain things. You have other cards that get buffed while they’re in your hand. It seems like you’re embracing the digital aspect of the game. You’re doing things that wouldn’t be possible in a regular card game.

Donais: We love doing stuff that isn’t possible in a regular card game. It lets us take advantage of our medium and get players excited about things they’ve never seen before. We tried it out first with Webspinner, one of the cards where you put a random beast in your hand. People seemed to love it, so we did a lot more of it in Goblins vs. Gnomes. This set naturally wants to have the random creature and minion mechanics. It was good for us to make sure that people love it and then just put a lot of it in. It’s been fun watching people and all their crazy videos and gameplays and playing with the cards. It’s worked out even better than we expected.