The challenge of maintaining class balance in Hearthstone's Arena mode

Class balance in video games is a delicate juggling act, and no one knows that better than the developers at Blizzard Entertainment.

Last week, the studio implemented plans to balance the Arena mode of its popular digital card game Hearthstone. In Arena, a player chooses from one of three randomly selected classes, then puts together the best deck they can from a series of random neutral and class cards. The rarity of cards determines how often they show up in the drafting phase. Commons show up more often than uncommons, rares, and legendaries, while class cards and cards from the latest expansion are more likely to show up than older, neutral ones. This means that classes with strong common cards, like Mage and Rogue, tend to perform better in Arena.

“As the game goes on, more and more people figure out which classes are stronger,” Mike Donais, senior game designer on Hearthstone, recently told Gamasutra. “The information trickles down and you see less variety in Arena, because people are playing classes that are perceived as, or are actually, the strongest classes, and that just makes it less fun.”

Here are just a few of the 45 cards that have been removed from Hearthstone's Arena draft

To help combat this problem, the Hearthstone team decided to remove 45 cards from the Arena draft. It took away a couple of the stronger cards from Mage and Rogue, like Forgotten Torch and Undercity Valiant, and it removed some underperforming cards from the other classes. Blizzard hopes this will cause more powerful cards to appear more frequently for the struggling classes, resulting in more robust and competitive decks.

“When you first enter Arena and are offered the choice of three different classes, our goal is that you can look at those choices and choose any class without feeling disadvantaged because of their difference in power level,” said Hearthstone designer Dean Ayala in a recent blog post detailing the changes.

There was a lot of debate amongst the Hearthstone team about which cards to ban and which to keep. It wanted to avoid removing strong spells and weapons, for example, because they create a lot of unpredictability and excitement during matches.

Players begin an Arena game by choosing from one of three random classes

“In general, we like having spells in Arena,” Hearthstone designer Peter Whalen told Gamasutra. “Spells create interesting game states. We also wanted to make sure that the iconic core cards that people associate with a class are kept in, so we’re more likely to restrict a card like the Goblin Auto-Barber than we are a card like Fan of Knives.”

To come up with its ban list, the team relied on the mountain of data it collects from millions of players in the form of business intelligence reports. The reports detail who’s playing what, how much they’re winning, what their win-rate would be with other classes, and more.

“We also have information on individual cards that helps us determine how we’re going to balance and move forward,” said Whalen. “How powerful is this card when you draw it? How powerful is this card in certain situations? How powerful is this card when you draft it? What kind of choice do you have to make? So, that helps us to inform our decisions as well.”

Out of Hearthstone’s nine classes, Paladin is the only one the team felt didn’t need an adjustment. It’s considered neither overpowered nor weak, but right in the middle. With the new changes, Donais hopes other classes will now be closer to its level. “We want every class to be included and participating,” he said.

During the drafting phase, players try to make the best deck out of randomly offered cards

But, at the same time, the team has to be careful with the modifications it implements. If it gives a weak class very strong cards, players will experiment with that class more. And while experimentation is one of the best aspects of a card game like Hearthstone, it can also lead to unforeseen consequences for the game’s balance.

“Honestly, it’s awesome when players come up with things we never expected, when they find new ways to use cards and build decks that we never thought they would,” Whalen said. “Of course, if they find something that’s wildly overpowered, then we’ll take steps. That’s not the best thing for Hearthstone. But having players come up with new, crazy things--that’s awesome.”

Right now, it’s too early to tell if Blizzard’s card bans are making a big difference in Arena mode, but Donais said the general response from the community has been positive. Removing weak cards from the underperforming classes has increased their win-rate, while the top two classes are now performing closer to the middle. Still, Donais said it will be a while before the team knows exactly how the changes will pan out.

“Even though the win-rates are closer, it will take some time before people start picking other classes and growing confident with them,” he said.

My Arena deck made short work of this Druid...

Blizzard’s efforts to balance Hearthstone are far from over. It’s an battle fought in small increments that’s likely to continue for the rest of the game’s lifespan. For other developers waging the same fight, Donais and Whalen offer this advice:

“Go with what’s fun and try to save what’s cool about each class when you’re making your adjustments,” Donais said. “If a class has its own unique identity, preserve that. Don’t try to make all of the classes able to do the same thing. Make them each amazing, but in a different way.”

“One of the most important things is finding the core identity for a class and sticking to it,” Whalen added. “It’s also more fun if all of the classes are very powerful instead of being very weak. If all of the classes are doing something that’s flavorful and exciting, and it feels powerful when you do it, but it’s actually fair and balanced when compared to the other things people are doing, that’s a better space to be in. It’s more exciting and fun when everything is strong.”