In my opinion Oscar's loss to Pac had huge impact on his legacy while others that are mentioned above (meaning Tyson, Ali etc.) are still mostly known from their good days. Maybe that loss will fade when Pac retires but at the moment when I think DLH; Larry Merchant's "This is embarrassing!" comes first to my mind.
Fights that ended in death or near-death injuries like Quiroga-Anifowoshe, Ruelas-Garcia, Mancini-Kim, Griffith-Paret 3, Pintor-Owen, Eubank-Watson 2, Benn-McClellan.
Of course mclellan, he was ahead on the score cards when the fight was stopped, even with a blood clot. He scored too knockdowns and deserves respect. He made a big sacrifice to boxing and even now dont regret it. What a warrior. Also fighters who have died in the ring dont have to live with the effects, they know fuk all, so god bless mclellan!