Two styles/weapons have proven effective (to some degree) against Floyd's shoulder roll: 1. Throwing caution to the wind and muscling Floyd on the inside while throwing numerous body shots and 2. An effective jab with the threat of a big punch.

Castillo and Maidana both proved very effective against Floyd by muscling him to the ropes and abusing his body while throwing a high volume of punches. This is much easier said than done however, as evidenced in Floyd's fights vs. Hatton and Jesus Chavez. A fighter needs to have brass balls/strong willpower to assume the necessary risk of exhaustion and getting caught with Floyd's counters to implement this style effectively. They also need to be stronger than Floyd but fast enough to close the distance and force Floyd to the ropes. The trouble Floyd had with Maidana n Castillo is the main reason I think guys like Duran, Pryor and Armstrong beat Floyd.

Oscar had success utilizing his jab from the outside, while his left hook kept Floyd tentative until Oscar gassed late in the fight. Cotto and Manny both had some success utilizing their jabs against Floyd, but neither committed to the jab or had the success that Oscar did. The Oscar fight in particular based on the trouble Floyd has with the jab is the main reason I see Floyd getting beaten by guys like Ray Leonard and Tommy Hearns.

Ray Leonard once said that he had success aiming his right at the top/exposed portion of Floyd Sr.'s head and would've done the same vs. Floyd Jr. That being said, understanding we are only talking shoulder roll here, Floyd DOES do MUCH more defensively than just that shoulder roll (slip, parry, duck, lateral movement, feint, set traps...etc.) and is PHENOMENAL at adapting during the fight, so I'm not sure that there is any one style/weapon that can beat him/his defense. I would've liked to have seen Floyd vs. prime Oscar and Mosely, Kostya Tszyu and Paul Williams (NOT saying he ducked ANY of those guys, just think those are GREAT match ups) to see if they could've figured his style out.