I am trying to identify a martial arts movie that I saw years ago. The hero gets into a fight with several bad guys, is defeated and one of his arms is cut off in the fight. Later he plunges his remaining hand into a jar of some potion to make his fist impossible to beat. Does anyone know this one?
Just so this question doesn't go unanswered: As JohnP mentioned, One Armed Boxer from 1971 might fit your description. The hero loses his arm in a fight, then plunges his other fist into fire and then into a special potion to make it invincible. The entire movie is available here on Youtube; The vase containing the herbal remedy appears around minute 56 and his fist is dipped in 59:30.