The blood god Hakkar is apparently not happy about all of the fun “Hearthstone” players are having with the Rastakhan’s Rumble expansion. So, he’s unleashed a curse upon the digital collectible card game, developer Blizzard Entertainment announced in a blog post on Tuesday.

“Oh yes, Hakkar has dabbled in Rastakhan’s little game—but in his dark heart he dreams of a return to the glory days, when every sacrifice in Gurubashi Arena was made in his honor and he ruled over the Gurubashi Empire with cursed blood and an iron fist! Er, scythey-claw-hand-thing,” Blizzard said.

A small number of “Hearthstone” players are already marked by Hakkar’s curse (including yours truly). The curse is a special card back. Each time a marked person completes a match with the card back equipped, the curse spreads to their opponent. How long will it take to infect all of “Hearthstone?” Who knows!

The Curse of Hakkar event is reminiscent of an infamous piece of “World of Warcraft” history. When Blizzard first introduced the troll-themed Zul’Gurub raid in 2005, its end boss, Hakkar the Soulflayer, cast a contagious hit point-draining debuff called Corrupted Blood on players. It was only supposed to last seconds, but thanks to a bug it soon spread it across all of Azeroth and killed thousands of lower level players. Regular gameplay ground to a halt as players tried to avoid the deadly debuff. The virtual pandemic lasted an entire week before it was patched out of the game. Some epidemiologists later used it as a case study for how a real-world epidemic could affect human populations.

“Hearthstone’s” Rastakhan’s Rumble expansion went live on Dec. 4 and added 135 new cards to the game, along with the new “Overkill” keyword, Spirit and Loa cards, and more. It’s the tenth full expansion to come out since “Hearthstone’s” launch in 2014.