According to Star Wars legends, Plo Koon fought a duel with Savage Oppress. He only lost because Oppress had managed to remove Koon’s antiox mask and render him incapable of breathing normally away from his home planet’s atmosphere. To put this in perspective, in Star Wars: The Clone Wars, there is a scene when Oppress manages to kill a Jedi, his Padawan, and several clone troopers with ease.