How does Blizzard create Hearthstone's incredible boss encounters?

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Ever since they were first introduced in last summer's Curse of Naxxramas add-on, we've been impressed by the single-player boss encounters in Hearthstone, a traditionally competitive multiplayer-focused game.

What's special about Hearthstone's bosses is not only that they're challenging encounters that force players to rethink strategies and often build completely new decks. But on top of functioning within this card game, they also work as clever throwbacks to raid and dungeon encounters from World of Warcraft, the MMO that Hearthstone is based on.

This led us to wonder about Blizzard's approach to these complex fights. How does the developer create encounters that simultaneously fit the needs and balance of a card game and the necessities of lore and nostalgia?

Today, the current Hearthstone adventure add-on, Blackrock Mountain, opens its fourth wing, Blackwing Lair. We spoke with Hearthstone's senior game designer, Ben Brode, about how each boss in this wing was chosen and how the team shaped those encounters across multiple attempts.

SPOILER WARNING: The following feature contains full details of the mechanics and, yes, even a big plot twist in this week's wing of Blackrock Mountain. If you haven't played it yet and want to stay surprised, bookmark this and come back to read it later!

    The bosses of Blackwing Lair

  1. The First Steps

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    The First Steps

    After finishing work on the Curse of Naxxramas adventure, Brode and his team spent a lot of time trying to figure out how to follow it up and digging into World of Warcraft's past to see what might fit best.

    "One of the ideas we had was Molten Core," Brode says, referring to the very first World of Warcraft raid. "World of Warcraft was doing its 10-year anniversary and bringing back Molten Core. But there just weren't 15 bosses there. How do you do an adventure with just nine bosses?"

    Instead of focusing on Molten Core, Brode looked at the wider area surrounding that raid: Blackrock Mountain.

    "I thought, 'what if we mixed it up and did a greatest hits?' There's, I dunno, 40 bosses in Blackrock Depths, but they're not enough to ground an adventure. What if we did just the coolest parts of Blackrock Depths?

    "We chose, I think, the coolest fights from that era of World of Warcraft."

  2. Gathering a Party

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    "The whole team got into a raid together in World of Warcraft"

    Gathering a Party

    After settling on Blackrock Mountain as a setting for Hearthstone's latest adventure, the next step for the team was to actually play through that old content together.

    "The whole team got into a raid together in World of Warcraft and went through the whole mountain," Brode says. "We split up into five-man groups and did Blackrock Depths and Blackrock Spire. We raided Molten Core together as a huge group. We did Blackwing Lair and Blackwing Descent. We even did the one part of Blackrock that's not in the Hearthstone version, which is Blackrock Caverns."

    As the overleveled team blew through this old content, Brode explained how the mechanics had worked back in the day from memory, urging everyone to try to zero in on what was cool and memorable about each individual fight. Meanwhile, the art team would lag behind, taking screenshots of each location to try to come up with unique ideas for a new game board.

    "I did e-mail the World of Warcraft team," Brode says. "I heard around the water cooler that we were updating Blackrock Spire for the Warlords of Draenor expansion. So I asked them what was going on with that and if there was anything cool we could use from that update."

    Eventually, Brode and the Hearthstone team decided to stick to the classic Blackrock Mountain that players would reminisce about. "We felt like what we did is what most people had in their mind when they think of Blackrock Spire," he says.

  3. Boss #1: Razorgore the Untamed

    "This was the hardest fight to design in all of Blackrock Mountain"
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    Boss #1: Razorgore the Untamed

    As the very first boss of the Blackwing Lair raid in World of Warcraft, Razorgore the Untamed was an immediate wake-up call to uncoordinated teams. Rather than simply defeating the boss, players had to use an orb to mind control Razorgore and then use him to destroy a room full of dragon eggs before they hatched.

    Razorgore proved to be a wall for Brode as well. "This was the hardest fight to design in all of Blackrock Mountain," he says. "Usually when I'm translating a fight from my World of Warcraft memories to Hearthstone, I try to find the essence of the fight. For me, Razorgore is about you getting to play as the boss."

    Initial designs for Razoregore in Hearthstone tried to get this across. Brode recalls an early version of the fight where the player's regular hero power was removed and replaced with a power called "Orb of Domination" that allowed players to take over as Razorgore.

    "You mind-controlled Razorgore, and you filled his side with eggs, and you have to kill the eggs, and then you win as Razorgore," Brode says. "But it felt a little weird that Razorgore was winning. So then we thought maybe you kill the eggs, and then you get Razorgore back as the enemy, kind of like the fight in World of Warcraft.

    Eventually, Brode and team moved away from this setup, which he called too "designer-y." He explains: "It's where a fight does the things we want it to do, but it doesn't feel elegant. It doesn't feel like a really solid experience. It's a bunch of disjointed mechanics that don't boil up into something that feels complete."

    Brode describes another complex iteration of the Razorgore fight where players swapped back and forth between playing as Razorgore fighting whatever their hero class was and the regular hero fighting Razorgore. "That was totally bizarre," he says.

    Finally, Brode moved away from the idea of controlling Razorgore and looked at something else defining about the raid encounter: the room full of eggs.

    "That's kind of the primary thing," Brode says. "You must destroy the eggs. So we switched it all around and made this fight where he's got a ton of eggs, and you have to get them. If you just let them sit, they're going to hatch and turn into these chromatic drakes."

    Razorgore's fight in Hearthstone is now driven by these eggs. His hero power summons a Corrupted Egg and gives all others on the field one more health. Once an egg reaches four health, it hatches into a Chromatic Drake, a new minion created specially for this fight that has a painful seven attack (though only three health, on normal difficulty at least).

    "Even though the mechanics of the fight in World of Warcraft didn't translate perfectly, the lore and the feel and the idea of this egg farm that you have to go and destroy — that ended up translating really well," Brode says.

  4. Top-Down Versus Bottom-Up

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    Top-Down Versus Bottom-Up

    The struggles to pin down Razorgore highlight a common issue in the process of creating single-player Hearthstone encounters. "There's kind of two ways to design both cards and missions," Brode says. "We call them top-down and bottom-up."

    As an example of top-down design, Brode points to Gothik the Harvester, an encounter from the Curse of Naxxramas adventure. It's a fight where they looked at the World of Warcraft version — which had players divide into a "live" group and a "dead" group to fight different enemies — and they designed the Hearthstone fight "specifically to hit that fantasy," in Brode's words.

    For bottom-up design, he brings up General Drakkisath, a boss from the third wing of Blackrock Mountain. "Drakkisath in World of Warcraft doesn't do a whole lot of stuff," Brode says. "He cleaves, and he hits hard, but those aren't interesting mechanics that translate into a Hearthstone fight. So we had a cool idea: What if every card costs one mana? You have to build a totally different deck for that. That's really weird and interesting. It's not really a Drakkisath design; it's a cool design that we put on Drakkisath."

    The ideal fight in Brode's eyes is a balance between these two design styles: "The best case is when you have a top-down design that feels like a crazy bottom-up design where yo want to build your deck differently.

  5. Boss #2: Vaelastrasz

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    "It feels like cheating"

    Boss #2: Vaelastrasz

    The next boss, Vaelastrasz, completely hits that top-down/bottom-up balance that Brode seeks. In World of Warcraft, this red dragon was actually initially an ally who was corrupted by Blackwing Lair's big bad, Nefarian. Before being forced to turn on curious raiders, Vaelastrasz would give players a massive buff increasing mana and energy regeneration — a final boost to make sure they could stop him before he turned against his will.

    In the case of Hearthstone, that giant buff is reimagined as "Essence of the Red," Vaelastrasz's hero power, which auto-casts at the start of each turn and causes both players to draw two cards. Essentially, for this fight you're going to get three cards every turn instead of one.

    "It speaks really well to the World of Warcraft fight, which gave you infinite mana regen or energy regen, and you just felt like you were super powerful," Brode says. "That feels like a really cool and simple mechanic design, but also a really top-down design from how it feels in World of Warcraft."

    Since card draw will be out of control for this fight, Brode believes many players will end up creating new decks just to take on Vaelastrasz. "It changes your deck," he says. "It changes the way you're playing. It feels like cheating, and yet the whole fight is balanced around this base-level rule change."

    Brode also warns that the player isn't the only one benefiting here. Vaelastrasz is also drawing three cards every turn and has a deck built to take advantage of this — including a special new spell card called Burning Adrenaline that costs zero mana and deals two damage to the player's hero.

    "He's always keeping pressure on the enemy hero," Brode says. "His deck is pretty good at taking advantage of this new crazy world and using cards that players don't have access to. So players have to figure out even better than him how to build a deck that takes advantage of this crazy new power."

  6. Boss #3: Chromaggus

    "This is one of the most unique fights in Blackrock Mountain"
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    Boss #3: Chromaggus

    Though he looks almost like a Cerberus-style, multi-headed dog-type creature, Chromaggus is actually a mutated dragon beast created by Nefarian's experiments. Within this creature rests the power of all five of World of Warcraft's dragonflights, and those powers manifest as five different powerful debuffs that a brave raiding party must learn how to deal with.

    "To me, that's the core experience of that fight — dealing with these different debuffs based on all the different dragonflights," Brode says. "I'd been thinking for a while about the idea of cards that can trigger while they're in your hand or basically act as debuffs while they're in your hand. I felt like Chromaggus was a good opportunity to do this."

    In his Hearthstone form, Chromaggus will summon a special Brood Affliction card into the player's hand every turn. The effects of these cards range from damaging the hero to healing up Chromaggus, to making his minions cost less to summon. These cards will remain active as long as they're in your hand, but players can choose to get rid of them at the cost of one mana each.

    "This is one of the most unique fights in Blackrock Mountain," says Brode. "Do you want to spend the mana to dispel yourself? Or would you rather spend the mana to play your normal minions and spells? It's a design space that we haven't really done anything else with except these adventure cards."

    The Hearthstone team plans to carefully monitor how players react to the Chromaggus fight to see if these kind of debuff cards might be something they want to explore more in the future, possibly through cards players can use against each other. But it will require balancing, just as the Chromaggus fight did.

    "These went through a lot of iterations," he says. "They're pretty complicated, and there's nothing else really like it, so it was hard to figure out whether it was fun to play against and cool and understandable."

    In one earlier form of the Chromaggus fight, the cards acted more as debuffs to the player hero rather than buffs to Chromaggus — making minions cost more and such. According to Brode, this version of the fight ended up feeling "too stifling."

    There was one other form of the Chromaggus fight that almost happened. In the World of Warcraft fight, he can actually turn people into chromatic dragonkin. This aspect almost made its way to Hearthstone as well.

    "We had a version where he would turn the player into a chromatic dragonkin, and your hero power became really bad," Brode says. "It was one mana to discard a random card. But it turns out that against Chromaggus, you have a lot of cards in your hand you don't want, because they're hurting you. The afflictions cost a little bit more to get rid of in that world too, so it was a cheap way to get a chance at dumping them."

    In the end, Brode decided to stick with focusing on just the debuffs. "It was a little too complicated when we were turning players into different things," he says. "It got more and more fun over time."

  7. Boss #4: Nefarian

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    "It's a total departure from World of Warcraft."

    Boss #4: Nefarian

    Nefarian is the big bad. He's the final boss of Blackwing Lair and the evil force behind the mountain as a whole. So ... why is he showing up in week four of the adventure rather than week five?

    "Nefarian is also the final fight of the final wing," Brode says with a laugh. "It mirrors the World of Warcraft story in some ways. In World of Warcraft, after you take out Nefarian, eventually he comes back to life. He's born again more powerful than before. We're going to see something happen along those lines."

    As the final boss of a raid, Nefarian's World of Warcraft encounter is fairly complex. But Brode points to one particularly memorable power: At random, he will take a certain class' abilities and turn it against every member of that class in the raid. Druids will get stuck in cat form. Mages will find themselves uncontrollably turning allies into sheep. Hunters will have their ranged weapons broken in an instant.

    In Hearthstone this translates to Nefarian's one-cost hero power, Wild Magic, which puts a random spell from the class of whoever he's facing into his hand. And it can be any spell that your class uses, not just one that's in your current deck.

    "It's cool and also in a weird way makes you think about your hero choice," Brode says. "Maybe I don't want to play priest against Nefarian, because he keeps getting mind controls and thought steals. Who has the worst spells? Maybe I want to play shaman and hope that he just gets totemic might."

    There's one other twist to the first Hearthstone battle against Nefarian, and it's one that the whole Blackrock Mountain adventure has been building toward. Initially the adventure began with Nefarian on your side, urging you to take out Ragnaros. Now that you're going up against Nefarian, Ragnaros is back ... and he's on your side.

    "This fight is really you plus Ragnaros versus Nefarian," Brode says. "Every turn in the fight, Ragnaros is going to send you some help from the Firelands. He's sending you Sons of the Flame and Lava Elementals and Ash Elementals. They're super good cards for really cheap that you can play to help augment your strategy, because Nefarian is an insanely powerful dragon that otherwise you would have no chance against."

    Brode notes that from a story standpoint, this is "a total departure from World of Warcraft." However, he also believes it's just bringing something forward that was always there.

    "Really, we have two masters of Blackrock: Ragnaros and Nefarian," Brode says. "This rivalry between them — that didn't come to the forefront ever in World of Warcraft, because they were never in the same place at the same time."

    As his team continues planning new adventures for Hearthstone, that ability to have plot twists and dig deeper into lore, even while keeping the storytelling light, is important to Brode. "I'm just a huge fan of World of Warcraft," he says. And he wants that passion to come out in each of these boss encounters.

Gameplay Walkthrough: Griffin and Phil play through week three of the Blackrock Mountain adventure add-on for Hearthstone