When it comes to attacks of the fist, kick, or weapon, Dook Goo Kau Bai might indeed by practically invincible, but what does he have in his bag of tricks to deal with poison attacks? The likes of Ding Chun Chou and West Poison Au Yeung Fung are not limited to hand/foot/weapon martial arts, but also use poison. It's not exactly honorable and using it to win over Dook Goo Kau Bai wouldn't really be a win in the fair sense, but nonetheless, what could DGKB's swordsmanship skills do against attacks by poison, especially the liquid and gaseous types (he can easily repel poisons delivered by palm or poison dart)?