I recently learned about the dangpa which is a Korean version of the trident. Supposedly there are Korean arts that utilize it. Anybody familiar with any of the arts that use the dangpa?
No specific arts for it; it was an Army weapon. According to a Korean site, it was taken into interest against the Japanese invasions in the chosun period because, although much shorter than an average spear, its multiple blades caught and degraded blades very well. Remember, at the time of the weapon's use martial arts wasn't even a thing for Korean civilians, only for the military.