In "One Flew Over the Cukoo's Nest," what does McMurphy see Nurse Ratched transform into? What is unusual about McMurphy?

Are you asking in a figurative or literal sense?

The end sees the dreaded Nurse Ratched brought down. Her new uniform shows off her large breasts and her power (namely, her terror and authority over the inmates) taken away.

What is unusual about McMurphy? Several things, the chief being is that he may not actually be crazy. He is not like the other inmates in that he goes against the rules whenever he can. He fights and undermines the nurse at every turn, but he does not actually see Ratched's final transformation, as that happens after his lobotomy and death. He does strike several blows against her authority throughout the course of the novel.