For those that are lazy, I'll run your memory. Hanged Man was a Part 3 stand that can travel between any reflection, and attack people in the reflection, while not appearing in the physical world. The attacks from the reflection damage the person in the real world. Hanged Man can also travel at lightspeed since he is riding a beam of light to travel between reflections ("https://jojowiki.com/Hanged_Man#Abilities").

So say we put Hanged Man against Pucci right before the universe reset, when they are in the ocean. The ocean is a massive reflective surface. Since both are moving at the speed of light, this is a matter of who has a more powerful ability (regardless of speed.) This goes to Hanged Man, as he has so many angles of attack in the ocean that Pucci, despite being at the speed of light, would not be able to keep up. Hanged Man simply stabs Pucci in the back and it wraps.