Hearthstone is walking the icy trail towards its next expansion, Knights of the Frozen Throne. In addition to 135 new cards, the game's nine original heroes are getting Death Knight versions of themselves through a new mechanic called Hero cards.

Neither minion, nor spell, the Hero card not only offers up a cool new look, but an amplified Hero power that keeps games intense well into the late turns. There's potential for excitement and possibly brokenness, so Shacknews wanted to learn more about the Hero card mechanic. To do so, we spoke to Principal Game Designer Mike Donais and Senior Concept Artist Jerry Mascho.

Shacknews: Going off the reveal with Ben Brode a few weeks ago, can you explain how the Hero cards work?

Mike Donais, Principal Game Designer: Hero cards are going to replace your Hero when you play them. There's nine of them, one for each classic Hero. Deathstalker Rexxar is the first one that we've shown. You pay mana cost out of your hand. He's not a spell, he's not a minion, he's a new card type, which we call the Hero Card. When you play it, it'll give you some armor. Deathstalker Rexxar has 5 armor. They all have a Battlecry effect, plus they replace your Hero power with a cool new Hero Power.

Build-A-Beast, as we've seen, is you craft a custom Zombeast, which we've never done before. Flavor-wise, it's Rexxar finding these animals and making better animals out of them. Like if you take a shark and a bear and you put the shark and the bear together, you get a sharkbear and it's twice as good! So that's what you do when you build a beast, you combine them together to make a better beast.

Jerry Mascho, Senior Concept Artist: My favorite combination so far is Vicious Fledgling with Stonetusk Boar, so you get a Charge minion that Adapts every time it hits face.

Shacknews: From an artistic and mechanical standpoint, what are the goals with the new Hero cards?

Donais: From our standpoint, we definitely wanted to play up the fact that these guys are more than just Death Knights. You take the typical unholy frost and blood death knight and we're building on that, giving them the Sylvanas treatment. We really wanted to amp up the dark side of what these Heroes could be. You've been playing these guys for three and a half years and we wanted players to take that journey of becoming the dark side of these characters.

Shacknews: Will these operate similarly to Quest cards, in the sense that each Hero card will be designed with a specific play style in mind?

Donais: Not quite as strongly as the Quests. The Quests were very specific, in that you had a progress counter, you were doing something very specific to increase that progress counter, and when you complete it, you received a reward. These are more like legendary cards that you would find in the minion slot, where they do something really cool. Some of them you build more around than others.

For example, Deathstalker Rexxar doesn't require you to play a very specific kind of card in your deck. Like, you're not playing just Elementals or Deathrattle cards. It is a bit different than normal Hunter decks, in that you're playing control, survivability, stalling, which is a soft build-around, and it gives you a really strong late game. Once you get to the late game, you'll be doing crazy things with your Build-A-Beast power, so you can focus the rest of your cards on controlling the early game and making sure you last until you get to Deathstalker Rexxar.

Shacknews: How do you hope to introduce newer players and even veteran players to this card type? Is that one of the goals of the new single-player missions?

Donais: The missions are going to be really cool. They teach you more of the story of the Death Knights and Arthas. They give you some background of how he got where he is by telling you your own story. And it familiarizes you with some of the cards as you, because you'll be using some of the cards or playing against some of the cards.

Mascho: Plus you'll get a free Death Knight Hero card once you complete the prologue. Everybody gets that once their first mission's complete. A random one, anyway.

Shacknews: Yeah, that's something I want to ask. Why award a random one, rather than allow a player to choose their Hero card?

Mascho: It's really hard to know which one is the best when you've only played the Prologue and seen none of them. I feel like, whichever one you choose, you'll feel like, "Oh, I have no idea which one to pick. Which one's the best? Which one's the most fun one?" So you'll have a lot of regret after you pick the wrong one. I think this makes it sort of fair for everyone and you don't have to feel like you have to wait a month to wait before picking.

Shacknews: And it doesn't work like Quest cards, where you'll start with a Hero in your hand? Or is there a minion/spell effect that can influence whether you get one in your hand sooner or maybe reduces the cost?

Donais: No, they're more like the Old Gods, where you have these big expensive powerful cards in your deck like N'Zoth or Yogg-Saron, and when you draw them, it'll be a big deal. But you might not draw them. You can use cards like Tracking to help get to them faster, but there's no special way to specifically get them.

Shacknews: I know these new mechanics are tested in Standard first and foremost, but how do you expect the new Hero cards to work in Wild?

Donais: I think it'll be cool. I think it'll change a lot of how the gameplay works, because they're all powerful upgrades to your Hero power. It could give you a lot of late game, so one of the things I think it'll do for Hearthstone, is they'll make sure if you want to include them in your deck, you'll have a strong end-game win condition. Once you get to turn 10-20, actually having ways to win and end the game is really important, rather than hitting turn 40 and running out of cards and slowly burning down while your opponent does the same. So I like how you have a good effect on the endgame.

Shacknews: Given what the Hero card introduces, I want to go ahead and ask, will it be allowed in Arena?

Donais: Oh yeah, these will be just like finding, say... N'Zoth in Arena. Or like finding some other powerful legendary, like Ragnaros, Ragnaros Lightlord, or Sylvanas. If you find powerful cards in Arena, these are legendaries that'll be in the legendary spot. Pick a good one and good luck! Maybe you'll get a Death Knight.

Shacknews: So I'd like to put on my Disguised Toast hat for a second and ask about some of the interactions with the Hero cards. How will some of the cards that interact directly with Heroes, like Amara, Lord Jaraxxus, or Sir Finley, work with these new Hero forms?

Donais: Once you play a Hero card, it changes your Hero and their Hero Power. So you can play Sir Finley and change their power again. There's nothing stopping you from playing that or Jaraxxus. This isn't a basic Hero Power, so you can't upgrade it with Justicar Trueheart, but other than that, it's mostly how you'd expect it. You can play a thing and change it.

Shacknews: When I look at a new mechanic, like the Hero cards, the first thing that comes to mind is Un'Goro, the Quest cards, and the Rogue Quest coming out more powerful than anyone imagined. I'd like to ask, when you introduce a new mechanic like this, is there a concern among the team that you may have underestimated the ingenuity of the Hearthstone community and may wind up with a particular Hero that is too powerful?

Donais: I think it's very likely that one of the Heroes is too powerful. There's a lot of very powerful abilities on Heroes. They're exciting to us. We know that the community is going to find some awesome way to use them in some crazy decks. That's what a card game is all about: finding out what the best way to use cards is, combine them together in clever ways to make the perfect deck or the perfect combination of cards to make awesome plays.

I think that's exactly what the Quest decks did. Quest Warrior and Quest Rogue iterated a lot on the deck list, learned how to play the deck really well, and as they went along, the decks got even better and better. Even Quest Mage falls in that category. People are getting better and better at Quest Mage recently and creating better versions of the deck and having more success. And we want to let people do that. I'd rather have a bunch of cards that are pretty scary to us, are pretty exciting and powerful, and finding out one of them is too good than just have a bunch of cards out there, where none of them are exciting or powerful and they're all safe. The last thing you want is a new set of cards and they're all safe.

Shacknews: One last question, knowing that there aren't any card reveals until July 24, without spoiling anything, what specific Hero card should players be on the lookout for? What do you think is going to excite the community the most?

Donais: Personally, I'm very excited about the Rogue Hero Card. Valeera is a total badass... and probably busted. But we'll see.

There's a lot of exciting ones. Each one of them tells its own story and does it in a really cool way and will hopefully deliver on the dream of Icecrown and Death Knights and that whole story.

The Knights of the Frozen Throne expansion is expected to hit Hearthstone around mid-August. Look for card reveals to begin on July 24.