Sin Fang is the leader of the North Korean Mafia. He ambushed both Tim and Steph, as well as Violet, in Robin #173 and #174, very soon after Steph's return and while Tim still believed her to be an impostor.
Tim wondered why someone as accomplished as Fang was working for someone as unaccomplished as the thug Marcel Pincus, but the question remained unanswered. Sin Fang is a heavily scarred Korean man with a, well, fang. He travels with armed henchman.
Tim told Spoiler to leave, but she refused, throwing a smoke bomb and beating up one of the henchman. Tim jumped in front of her to save her from some flying knives, but was not badly injured. Fang continued to throw knives at them, but both Tim and Spoiler deflected them, Spoiler with an as yet unidentified sliver hooklike weapon.
Fang is an extremely accomplished martial artist, as he beat Robin, Spoiler and Violet all to a standstill, injuring Violet quite badly, and nailing both Steph and Tim with kicks to the stomach. Knives seem to be his preferred weapon. Only Tim calling his car in by remote control and knocking everyone out of the way to escape saved them. Steph refused to escape with Tim and Violet, and instead threw another smoke bomb to take care of the henchmen and grappled away. Fang attempted, as Tim put it, "to stab a CAR to death" but was thrown off.