Blizzard Entertainment‘s digital collectible card game “Hearthstone” has a new expansion coming on Dec. 4, and it’s bringing with it two new cards that pay homage to one of “World of Warcraft‘s” most infamous incidents, according to PC Gamer.

Hakkar, the Soulflayer is a 10-cost legendary that shuffles a Corrupted Blood card into each player’s deck. When it’s drawn, the spell deals three damage and shuffles two more copies into the deck. Hakkar could see some play in fatigue-based decks, where a player forces their opponent to take damage by running out of cards. But, it’s too soon to tell if it will make its way into the game’s meta.

Both cards are a reference to “World of Warcraft’s” Zul’Gurub raid, which first launched in 2005. When players encountered and attacked Hakkar there, he would cast the highly contagious Corrupted Blood debuff, which slowly drained their health and spread from player to player. It was only supposed to last seconds and it wasn’t supposed to work outside of the raid area. But, a bug allowed players’ pets to carry the affliction to other areas. It caused a virtual pandemic that lasted for over a week, killing many lower level characters in the game’s cities and disrupting gameplay in the process.

Some epidemiologists later used the incident to study how infectious real-world diseases can affect a population.

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“Hearthstone’s” tenth expansion, Rastakhan’s Rumble, is based on “World of Warcraft’s” troll race and its lore. It adds 135 new cards, along with a new keyword mechanic called Overkill, which gives a bonus to players who deal more damage than necessary to destroy a minion.