1. Natural ability/talent. 2. Hard work in the gym to add skills to his Natural ability/talent. 3. He rarely makes a mistake in the ring. When he dose he adjusts. 4. Ecomany of movement. He dose not waist movement this includes how he moves around the ring and avoids punches. As well as to how and when he throws punches. 5. Timing and speed. His timing is among the best of all time if not the best. He is very fast as well.
Mayweather is cerebral, calculated, highly skilled, versatile, accurate/places his punches, is very hard to catch clean, and trains like a ****ing animal. The genetics are in his favor, as well. Add all of that up and you have an all time great fighter.