In an effort to further players' enjoyment and create common goals for large groups to accomplish, game developers added World Events into the game. The first world events were outdoor raid bosses that could be challenged without entering an instance. These bosses were the blue dragon Azuregos of Azshara and the Burning Legion demon Lord Kazzak in the Blasted Lands. These were followed by four green dragons corrupted by the "Emerald Nightmare." In addition, certain areas of Azeroth experience an "elemental invasion" where waves of elemental-class monsters will run rampant for a time or until they are destroyed.

 

Blizzard has also implemented holiday content. Valentine's Day, Easter, Independence Day, Oktoberfest, Halloween, Thanksgiving, Christmas, as well as New Year's and its lunar counterpart all have their Warcraft-themed counterparts. During these week-long events players partake in holiday-themed quests usually involving humorous references to real-world pop culture surrounding the holiday. For example, one of the Winter's Veil (Christmas) quests involves fighting a creature known as the Greench (a parody of the Grinch) and rescuing a kidnapped reindeer named Metzen (styled after lead designer, Chris Metzen). Some world events are designed to repeat themselves on a regular basis such as the Darkmoon Faire. Others have been a one-time event that marked a large change in the in-game world like the opening of the Gates of Ahn'Qiraj, the Scourge Invasion and the opening of the Dark Portal which signaled the beginning of The Burning Crusade expansion, along with other less notable events.[25]

 

 

 

The Corrupted Blood plague incident was one of the first events to affect entire servers. Patch 1.7 saw the opening of Zul'Gurub, the game's first 20-player raid dungeon where players faced off against an ancient tribe of jungle trolls under the sway of the ancient Blood God, Hakkar the Soulflayer. Upon engaging Hakkar, players were stricken by a debuff called "Corrupted Blood" which would periodically sap their life. The disease would also be passed on to other players who were simply standing close to an infected person. Originally this malady was confined within the Zul'Gurub instance but made its way into the outside world by way of hunter or warlock pets that contracted the disease.

 

Within hours Corrupted Blood had infected entire cities such as Ironforge and Orgrimmar because of their high player concentrations. Low-level players were killed in seconds by the high-damage disease. Eventually Blizzard fixed the issue so that the plague could not exist outside of Zul'Gurub.

 

The corrupted blood plague so closely resembled the outbreak of real-world epidemics that scientists are currently looking at ways MMORPGs or other massively-distributed systems can model human behavior during outbreaks. The reaction of players to the plague closely resembled previously hard-to-model aspects of human behavior that may allow researchers to more accurately predict how diseases and outbreaks spread amongst a population.