The Moon Guard Arthas attack, a famous hoax on the Moon Guard US server, was initiated by a group of players using the Ethereal Soul-Trader loot. The group was able to convince the entirety of the Moon Guard server that Stormwind City was being attacked by Arthas, who, in this manifestation, was a giant swarm of purple energy balls.
Ashamal, Lethan, Tobiathin, Quinlinne, and Kenki were the masters of the plan. Through general chat, they were able to convince the world, through the swarm of the purple energy behind them, that Arthas was sending AoE attacks for random players, and was yelling about destroying Stormwind City.
Raids of players gathered at Goldshire to defend their Kingdom, mass hysteria was invoked by the display of chaotic effects, swarming crowds of players, and the constant yelling in general chat.
"'Twas the first day that a WoW server was rickrolled." - Aphel