Last month, Blizzard Entertainment unleashed a curse upon the unsuspecting player base of its popular digital collectible card game “Hearthstone.”

The developer chose a small number of content creators and journalists to receive the Mark of Hakkar, a special card back based on the winged blood god of the same name in “World of Warcraft” lore. The dark loa is worshipped by the Gurubashi trolls, the fantasy race at the center of “Hearthstone’s” latest expansion, Rastakhan’s Rumble.

Once those “patient zeroes” equipped the cursed card back and started queuing up some matches, they began “infecting” the community with it.

“We’ve been dreaming of this mechanic, where players can infect card backs upon other players, for a long time. A year or more,” Pat Nagle, “Hearthstone’s” lead live content designer at Blizzard Entertainment, told Variety. “We were waiting for a good chance or a good time to bring it out, and with this expansion it just seemed like the perfect time because Hakkar’s in the expansion. The stars just kind of aligned.”

Jay P. Morgan

The Curse of Hakkar event started on Feb. 5 at around 4 p.m. Eastern. At that time, about 4% of the North American “Hearthstone” player base had the mark. One hour later, the curse reached 20% of the population. By 6 p.m. Eastern, more than half (66%) were infected. By 11 p.m., less than 12 hours after the event’s start time, Hakkar’s mark spread to 87% of North American “Hearthstone” players, where it seems to have maxed out.

Hakkar’s curse struck Los Angeles the hardest in the first 24 hours, according to Blizzard. Toronto was the second-most corrupted city in North America, followed by Chicago, Montreal, and Houston. Seattle, Dallas, San Francisco, Atlanta, and New York rounded out the top 10.

While Blizzard didn’t name names, it said the “Hearthstone” player who corrupted the most people in North America infected a total of 63 accounts. In Europe, the person who infected the most players corrupted 58 accounts.

“When we developed the mechanic of spreading the card back, we thought a lot about how we would handle our patient zeroes, because we knew that was going to have a big impact on just how fast the thing spread,” Nagle said. “We went back and forth on whether or not we wanted it to spread really slow or really fast. We thought fast would be the most impactful. But having said that, I think it spread a little faster than I thought. We wanted it to go fast, but it beat my expectations.”

The Curse of Hakkar event is a nod to one of the most infamous moments in “World of Warcraft” history. When Blizzard launched the Zul’Gurub raid in 2005, featuring Hakkar the Soulflayer as its end boss, it accidentally unleashed a virtual pandemic that killed massive amounts of lower level characters.

One of Hakkar’s attacks was a highly contagious debuff called Corrupted Blood that drained a character’s hit points over time. While the spell was only meant to last seconds — and only within the confines of the raid zone — a bug allowed players’ pets and minions to carry it into the wider game world, where it quickly spread. Large piles of skeletons accumulated in “WoW’s” major cities. Normal gameplay was so disrupted many people simply chose to not log on until the situation was resolved.

Nagle was working on “World of Warcraft” as a world events designer at that time. “It was just a big mess everywhere,” he said. “We must’ve fixed the bug really fast, but when it hit, it hit really hard. It had a big impact and everyone remembers it, so we really wanted to do it [in ‘Hearthstone’].”

Blizzard Entertainment

The Curse of Hakkar is also notable for another reason — it’s the first “Hearthstone” event that’s based on the current expansion. Blizzard followed it up with another thematically appropriate event called Season of Rastakhan. It encouraged players to compete in three weeks worth of Tavern Brawls, and rewarded them with free Rastakhan’s Rumble card packs.

Crafting a more narrative-focused experience around expansions seems to be a major goal for Blizzard. It recently laid out its “Hearthstone” plans for 2019 and it’s promising “something bigger, deeper, and much more ambitious than anything we’ve ever done.” That includes a solo adventure which launches about a month after the first expansion. It will be broken up into chapters and will let players master new systems and mechanics from the perspective of a mysterious, yet familiar, new Mage character. While Blizzard hasn’t released details on the next expansion just yet, many expect to see it within the next two months.

As lead live content designer, Nagle said he and his team are excited by the thought of slowly unraveling a cross-expansion storyline via more events like the Curse of Hakkar. “We want to keep doing that,” he said. “Bring events that help drive the narrative of our expansions.”