My khajiit in Elder Scrolls Online. In a previous RP guild in there, I had an encounter with a villain who wielded a sword called the Duskbreaker which was enchanted with powerful umbral magic and took it. At the time, my khajiit was still a vampire and his sire would affect him telepathically, even after he was cured from the vampirism. His current guild managed to kill his sire and now the khajiit is being mentally corrupted by the sword like its predecessor, cleaving down on enemies and innocents alike, satiating the sword's bloodlust. My khajiit doesn't know it due to the sword giving him black outs. The reason why his serial killer name is 'Fog' is because the sword excretes a shadowy purple fog when it's active.