There is a corner of Blizzard Entertainment that is now obsessed with death. As we grow older we all start to dwell on our own mortality, of course, but this is different: the people making Hearthstone are excited about death, the process of dying and the effect death has on the ones we leave behind. I can hear it in their voices, speaking to me over the phone from thousands of miles away. They are excited about finally realising the potential of death - and particularly the potential of deathrattles.

Deathrattle is a mechanic in Hearthstone that activates when certain creatures are killed. The Leper Gnome, for example, is a cheap card that doesn't last very long, but its deathrattle gives it added bite: when it dies, it deals two damage points to the enemy hero, and in Blizzard's fast-paced card strategy game, where chipping health points away from the opposing hero is the main objective, that makes it rather potent. Yet there are only 11 cards out of 465 in Hearthstone that have a deathrattle. Curse of Naxxramas, the first major add-on for the game, is set to change that - hence the obsession.

"Almost all of the cards in Curse of Naxxramas have to do either with deathrattle, or things that happen when something dies, or things that interact really interestingly with things dying," says Eric Dodds, Hearthstone's game director. "The idea behind Naxxramas as a dungeon is of course that it was from World of Warcraft, ruled by the necromancer Kel'Thuzad, so we really wanted to jump big on the whole death and deathrattle idea, and we also really liked the idea of taking this mechanic which we'd done a little bit with and blowing it out and doing crazy stuff with it."

Naxxramas also features a new game board with lots of clickable elements. I am embarrassed by how exciting this is.

The concept of Curse of Naxxramas is similar to a WOW Raid - players enter the necropolis of Naxxramas and explore its five wings, facing off against computer-controlled boss enemies, each with their own unique cards and hero powers. Since most Hearthstone players left the game's primitive tutorials and AI battles behind ages ago, this will be their first taste of player-versus-environment for some time, so Blizzard is keen to get all the trimmings right, promising a new game board and charismatic adversaries. "I can tell you that Kel'Thuzad is going to be doing a fair amount of chatting," says Dodds, "and he totally cracks me up."

"We still feel very good about getting out this summer" Jason Chayes, Hearthstone production director

But I've played Hearthstone for hundreds of hours now, so I suspect that over the long term the most important thing about Curse of Naxxramas will be the 30 new cards it introduces, the potential they have to influence the meta-game - the dramatic swirl of popular tactics as people invent and copy each other's deck concepts - and how versatile they prove when it comes to building and disrupting strategies that are built not just around the new cards, but also the hundreds of existing cards that I already know intimately. Like Wes, I've grown a little tired of constructed decks, but this kind of seismic change should pull me back in.

We've only seen a fraction of those 30 cards so far, but they're already firing the imagination. "There's a bunch of cards that work in super-interesting ways," says Dodds, who notes that the simple Nerubian Egg - a cheap card with little health and no attack - is fantastically versatile thanks to its deathrattle, which spawns a Nerubian (a kind of spider) with four attack and four health points. "It's a card that we've seen people build decks around, with other [existing] cards that give the Nerubian Egg an attack so you can make sure you get that Nerubian Egg killed." Opponents who rely on area-of-effect attacks will want to avoid killing it with the deathrattle active, too. "It's a particularly powerful card against Hunters who use Explosive Trap a lot," Dodds notes.

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One of the most eye-catching cards is the new legendary card (legendary meaning it's very rare and can only be included once in your deck) called Baron Rivendare. A mid-cost card with low attack and a ton of health, Rivendare causes your other minions to trigger their deathrattles twice if they expire while he's in play. "In a lot of ways I'm excited about that card because I don't know exactly how players are going to use it," says Dodds. "It's one of the types of card that we call a story card - it's a card that the number of possible combinations for it are crazy and once it gets out there we expect to hear some crazy stories that come out of it."

A simple example of that from Blizzard's internal testing involves an existing card with a famous deathrattle - Sylvanas Windrunner, who gives you control of a random enemy minion when she perishes. "Like, hey, I have Sylvanas out, and then put Baron Rivendare out and kill Sylvanas, and steal two of your creatures..." Deathrattles are going to be stacked to the rafters, then, and Blizzard's excitement about all the unintended consequences suggests the developer hasn't been worried about upsetting the balance of what's there already.

Pay to wing? Curse of Naxxramas takes you through the four wings of the Naxxramas necropolis before you face off with the mighty Kel'Thuzad in the Frostwyrm Lair. The Hearthstone wiki has a good roundup of the confirmed and unconfirmed possibilities along the way: The Arachnid Quarter - home to the oversized arachnid Maexxna, we may also run into Anub'Rekhan and Grand Widow Faerlina. The Plague Quarter - we know we will face Heigan the Unclean and the fungal horror Loatheb, but maybe we'll also see Noth the Plaguebringer. The Military Quarter - we know nothing about the enemies within at this point, but the suggestion is Instructor Razuvious, Gothik the Harvester and The Four Horsemen. The Construct Quarter - Patchwerk is going to be in there, a shambling abomination (although don't say it to his face), but maybe also Grobbulus, Gluth and Thaddius. Frostwyrm Lair - the frostwyrm Sapphiron and, of course, Kel'Thuzad.

"It's very important for us to throw a curveball out there and see the game changing in interesting ways," says Dodds. "We have a balance team of extremely high-level players and they're doing a phenomenal job of balancing these cards. It's certainly possible that there will be issues we have to deal with," he admits, referring to the possibility of tweaking card values, "but we're always paying attention and we're going to try to change as little as possible, and we'll see how that turns out."

Something that may make that easier (or more difficult, perhaps) is the way the cards will be distributed. Players won't get them all at once - the five wings of Naxxramas will be released week by week and the new cards can only be earned by playing through the content, which also includes separate class-specific challenges that each unlock a new class-specific card.

"When you are clearing a wing, each time you defeat a boss you get the card that's associated with that boss," says Dodds, who implies that Mindpocalypse, the card shown alongside the Plague Quarter boss Heigan the Unclean in the original reveal, will be among the playable cards. "When you have defeated the final boss of a wing, you get the card associated with that boss and then the bonus legendary associated with clearing that one." (It's not part of the plan to let us craft the cards using dust though, Blizzard tells me.)

"In the case of Poison Seeds we thought about, hey, we have Druids and we really like the idea of Treants and Druids and doing a little bit more with that, and while we want to have it be death-related, what's an interesting interaction we can have in the combination of those things."

Curse of Naxxramas is still a little while away. "We still feel very good about getting out this summer," says production director Jason Chayes. "We're not too far out from putting out an announcement." One thing that announcement timing may depend on though is the business model. Blizzard has already confirmed that the first wing (the Arachnid Quarter) will be free and that the subsequent four can be purchased with in-game gold or real money, but we haven't heard about pricing yet. We'll find out soon though.

"We should have an announcement with regard of the cost in the next few weeks," says Chayes. I also ask about the possibility of some sort of discount for buying all the wings at the same time and Chayes says it's "something we're discussing internally". "It is something we think could be a good way to acquire the entire Raid," he says (Blizzard's preferred nomenclature for this content is Adventure Mode, but it's kind of sweet to hear Chayes betraying his WOW-loving roots whenever he refers to it as a Raid). "It's definitely something we're looking at right now."

I also point out that most people just want to know how much gold they will need - whether they need hundreds, thousands or even tens of thousands in gold - and that players are hoping Blizzard will narrow down the costs soon.

"I think that's a very fair request," says Chayes. "Just like we've done with the core game right now, where you can acquire packs and Arena entry with gold as an alternative to real money, we want to make sure that that's an option available to players, and I think pricing wings in the tens of thousands of gold wouldn't necessarily be a realistic way to get people into a particular wing, so it is important to us that we're continuing to follow the philosophy of the existing version of the game so that both options are viable.

"In terms of exactly what those numbers are, we're still kind of looking at some more analysis internally before we say for sure, but I think the one thing all of your readers can expect basically is that we will definitely make it so both are realistic and viable ways to be able to get into the Raid." So you haven't really decided yet? "That's pretty much it."

While Blizzard umms and ahhs about dates and prices, then, the rest of us can get busy scheming about how best to die.