Kas the Bloody-Handed was the vampire lieutenant of Vecna and the original wielder of the Sword of Kas. After years of loyal service to Vecna, he became Kas the Betrayer. It is said that the sword itself whispered to Kas, convincing him to slay his master and usurp his power.
also, I’m sorry, but how did Eddie being killed have anything to do with the plot except for refusal for one of the main characters to die? and by bats? really? that’s it? And Dustin had to sit there by himself and what, all of them collectively decided to leave him there? And only Dustin talked to his uncle? Like, ok, I’d rather see him deal with a whole trial and end up in jail then whatever the fuck that was.