There's a question going around about how many times Marty McFly died during the course of Back to the Future.
The theory goes like this: There are two times in BttF2 and once in 3 where Marty was close to death and Doc saves him. Once on the rooftop with 1985 Biff where Marty jumps off of the building, once where Marty is hoverboarding away from 1955 Biff, and a third where Marty is strung up and being hung by 1885 Buford.
The first one, Marty saves himself by jumping from the top of the building and is saved by Doc, but how did Doc know to be there? The thought is that Marty dies on the rooftop, Doc finds out about it, goes back in time, and flies up to the building to save Marty's life.
The second one, Doc drops a string of flag banners just as Marty is coming out of the tunnel. Doc had no way of knowing where Marty would be. Marty was dragging behind Biff on the hoverboard, and came out of the same side of the tunnel that they went into. Marty was run-down by Biff, killed, and there was likely a memorial for poor Calvin Klein. The fun thing about this one is that BttF1's Marty would go forward in time to a different universe where his parents tell him about that poor Klein boy, run down by Biff the night that they met and fell in love.
The third one is tricky. In this one, Doc has no way of saving Marty if he dies because he's trapped in the 1885 with no time machine… or is he? So let's say that Marty dies at Buford's hands. Doc goes on an investigation to find the Time Machine, figures out a plan to get it up to 88 miles per hour, uses the same train trick that they use later in the movie to get back in time with the destroyed train and car so that he can go back, save Marty, and do it all over again. He did happen to have that plan worked out in an awful hurry.
The only proof I have of this third one is Clara. Doc knew where she would be and was VERY fast in getting to her rescue, much faster than a man of his years should have been. This means that he saves two people in the third movie in the after-effect of his stretch of time travel.