Kill Walton Simons with the Dragons Tooth Sword while he's also wielding a Dragons Tooth Sword. Simplest approach is to stay close to him by circling him, until his health is so low that he activates his cloak. Then wait for him to pull out his DTS and then kill him with your DTS. It took me a few tries because sometimes he just doesn't change weapon, so you have to evade his attacks and stay close until he does.