For those who don't know, ten years ago the MMO Runescape played host to one of the most infamous glitches in gaming history. A player called Cursed You had invited some friends to his in-game house once he had maxed his construction skill, but decided to eject them all from the premises.
Things turned sour, however, as a group of players marked as PvP in the house didn't lose this PvP flag when ejected, allowing them to storm through Falador and massacre whoever they pleased. The most notorious of these players was named Durial321.
This event went down in internet infamy and meant that many players lost their items when killed as well as the banning of those involved. To commemorate that day, then, Old School Runescape made Falador available for PvP once more on World 111 as a tournament server.
Before that, however, there was a server-wide message saying "Cursed You is having a 99 construction house party in Rimmington on world 111. He will level in 30 minutes". A giant version of Durial321 then arrived and the other players had to pitch in to kill him.