The Halloween 2k4 event took place on October, 31 2004.

Before Halloween, a strange individual known only as 'LabTechX' appeared in the Marketplace selling strange vials of a green, unknown liquid. Users, noting the strangeness of this, rushed to purchase the vials from the NPC. Users were left in suspense until Halloween, when Gambino opened up his mansion to host the event. At some point, the mansion's alarms went off and a lock down to occurred. Gambino made an announcement of it being just a false alarm, and everything went back to normal. Then, several NPC:LabTechs showed up at the celebration to have a retirement party for LabTech 062. Suddenly, LabTech 013, supposedly deceased for quite some time, rose from the dead and attacked several LabTechs, quickly initiating their transformation into zombies. The condition quickly spread, infecting all LabTechs, except LabTech123, who suspiciously didn't show up. Now the real alarm went off. The LabTechs, who during the retirement celebration were in a separate closed room, quickly broke free and started attacking the Gaia users who were attending the event, causing them to take on the zombie status as well. Gambino, who was starting to feel rather uncomfortable, issued shotguns to anyone who was not a zombie, and thus started a battle between humans and zombies. As it turned out, the mysterious vials were the key to fighting the disease, each vial having the healing power to get rid of the viruses that could be found in one bite. However, even with the weapons and vials, the virus spread too quickly and Gambino's head of security, Bucho, initiated the Silent Flash protocol. This caused a large missile to be launched from an unknown location on a course for the source of the threat, Gambino's mansion. The missile made impact, and the mansion was destroyed, ending the zombie threat. Cindy Donovinh, from Gaia 9 Action News, made her first appearance, and gave a report on the situation.

Besides the events at the mansion, the shopkeepers all dressed up in costumes for Halloween, and gave out candy. If one collected enough candy, they would then be able to trade it to Jack, a mysterious figure who represents the spirit of Halloween since 2003, for a grab bag containing a prize, but only after finding him wherever he was hiding in the world of Gaia.