Only five of the 30 new cards slated to be released for Hearthstone’s first single-player campaign–titled The Curse of Naxxramas–were officially unveiled at PAX East 2014 today. But if those cards are anything to go by, then it seems deathrattle is going to become a lot more common in Blizzard’s recently released card game.

Deathrattle (abilities triggered upon a Hearthstone minion’s demise) feature in four of the five new cards so far confirmed for The Curse of Naxxramas, and is apt considering the campaign’s eponymous setting. In World of Warcraft, Naxxramas is the floating necropolis of the archlich Kel’Thuzad–in other words, the undead have sway in this corrupted location. Players will be able to tackle this creepy area when The Curse of Naxxramas is released later this year, and marks the first of Hearthstone’s single-player-focused Adventure Mode releases.

So what exactly is Adventure Mode? In this mode, players will do battle against a series of AI opponents to gain new cards. The Curse of Naxxramas will have five sections or “wings” to play through, with each wing featuring anywhere from three to four bosses. Cards are earned as you defeat bosses, with bonus cards also being awarded for clearing wings. Any card earned will be usable in Hearthstone’s regular Play or Practice modes, while Naxxramas-themed cards will also be added to the mix in Arena matches. Only the first wing–the Arachnid Quarter–will be free. The subsequent four in Naxxramas will need to be purchased either through in-game gold or with real world money (although Blizzard has not confirmed what the cost will be). And your reward for completing all of Adventure Mode? 30 brand new cards, including class-specific ones earned by completing class challenges.

So how will the introduction of 30 new cards to Hearthstone affect the game’s balance? Lead designer Eric Dodds says balance is something Blizzard is continually monitoring, with a new team created within the company that continually monitors balance issues.

“Before we had done a lot of balancing by what we thought was the right thing to do, and we did some internal balancing, but because we were in beta, there was also a lot of balancing going in because the community was helping out a lot,” Dodds said. “But going forward, we now have a balance team making sure that all of these cards are balanced, because we have to make sure these are not cards that will break the game. So we have an internal team that is working on these specifically.”

Dodds says the introduction of 30 new cards also has the potential to significantly impact Hearthstone’s metagame. “What’s interesting I think is there will be an interesting metagame happening during those four weeks as new cards come out, and decks suddenly change. Everything will be different, and then a week later, all these new cards come out. So over the course of the month we’re going to see really interesting changes and shifts in the metagame.”

“One of the cards I’m excited about is Baron Rivendare, because it makes deathrattles trigger twice. There will undoubtedly be things that happen that honestly we haven’t even thought about as possibilities. There are certainly the simple ones where I have a harvest golem and I get two damaged harvest golems out of it. It’s one of those things that I expect interesting combinations to come out of the community.”

What happens, then, in the case of these new cards inadvertently unbalancing the game? Dodds says the solution is not to withdraw cards, but rather to empower players with solutions by introducing new cards into the mix.

“As far as card changes moving forward, our plan is, ideally, not to make any card changes because we want these cards to feel really solid in player’s hands. That said, if something is clearly very out of hand–and that’s a super subjective thing to say–then it’s something we’ll talk about,” he said.

“But really what we want to do is when we feel the environment changes and changes in a way that doesn’t work super well, is that we put additional cards out there in the player’s hands that allow the player to take control. Because really the way we think about it is that we’re just providing tools for the player to have a fun experience. So if it feels like they don’t have the right tools for that experience, then we better put some more tools out there.”

If you choose to never put in a dime, you can still access all of the content over time.

Hearthstone production director Jason Chayes.

For a game that has so far kept most of its gameplay modes free (buying cards and Arena are, of course, a different matter), the move to charging for a new mode is an interesting one for Hearthstone. But for production director Jason Chayes, the move still perfectly aligns with the game’s goal of allowing players to access content in whatever way they please.

“We basically wanted to make it that no matter how you were experiencing Naxxramas, you were able to unlock the various wings for free just by earning the gold and unlocking it. That’s an important philosophy we have for Hearthstone, is that if you choose to never put in a dime, you can still access all of the content over time. So that is a core part of how Naxxramas is designed. Beyond that, though, if a player is interested in getting to that content a bit faster, they can spend a bit more money and access it as well,” he said.

The Curse of Naxxramas is set for release sometime in “summer” 2014 for PC, Mac, and iPad.