I think there are three fights that can cement Mayweather's legacy in this order
1. If Pacquaio beats Oscar, then IMO Mayweather has to fight Manny to remain fighter of the decade.
2. Paul Williams or Miguel Cotto, both are viewed as Mayweather's potential biggest challenge.
3. Antonio Margarito: I think this is an easier fight then Cotto or P.Williams for Mayweather to be honest, but Margarito gets the credit of beating Cotto, and pretty soon Mosley.



One other one down the road is Andre Berto, I personally see Berto as the hardest opponent for Mayweather because of his unbelievable speed, I think Berto will cement his own legacy in the next few years by beating Clottey, Judah, Cotto, anyone around his size in the welterweight division. Then this would be a huge fight for Mayweather to come back to, but I am not sure if he will be able to beat prime Berto.