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Tear Jerker: Back to the Future
Both times that Doc gets shot in Part I. Marty's reaction might be a little Narmy to some, but...imagine seeing your best friend killed in cold blood, twice, and not being able to do a damn thing about it in either case.
Marty hugging Doc goodbye before trying to get back to 1985. Now more than ever, his mind is on whether his friend will get the message. If he doesn't, this will be the last time he'll see him alive, and Marty knows it.
Have a couple of tissues ready in Part II when Marty finds George-A's grave…
The scene when Marty receives the letter from Doc can cause some to get misty eyed, the music doesn't help either. It's not sad, it more or less causes tears of joy.
In the second movie, there's a scene when Jennifer finds out that Marty had a car crash thirty years ago, from racing Needles when he called him a chicken. This crash broke Marty's hand, which left him unable to play guitar very well, and forever crushing his Rock Star dream. Then we see Future!Marty silently playing his guitar.
The song Marty is playing? "The Power of Love" from the first film.
"Besides, they couldn't match up the bullet that killed your old man!"
"You son of a bitch," indeed.
The full reading of Doc's letter (which was started at the end of Part II but never finished), especially since it was intended by Doc to be the final words he ever said to Marty:
"Do not, I repeat, do not attempt to come back here to get me. I am perfectly happy living in the fresh air and the wide-open spaces, and I fear that unnecessary time travel only risks further disruption of the space-time continuum. And please take care of Einstein for me. I know that you will give him a good home. Remember to walk him twice a day, and that he only likes canned dog food. These are my wishes; please respect them and follow them.
And so Marty, I now say farewell and wish you Godspeed. You've been a good, kind, and loyal friend to me. You've made a real difference in my life. I will always treasure our relationship and think on you with fond memories, warm feelings, and a special place in my heart.
Your friend in time,
"Doc" Emmett L. Brown.
September 1, 1885."
Big one in Part III when the DeLorean gets destroyed. Seeing one of the most iconic props in cinema wrecked after it has gone through hell and back and just keep ticking is heartbreaking. The worst part is seeing the flux capacitor and the time interface go out.
Marty:Well, Doc, it's destroyed…just like you wanted.
Seconded. That car was practically a main character by itself. A more faithful vehicle you couldn't hope for. And it was smashed to smithereens like any other piece of junk. When Marty chokes up, we choke up too.
A deleted scene in Part III shows Marshall Strickland gunned down by Mad Dog Tannen, right in front of his son. He dies on the spot. It was actually for this reason the scene was taken out, though the event has been confirmed as canon, thanks to the game.
Any scene with Doc and Clara within thirty feet of each other that is not a Crowning Moment of Heartwarming is bound to be a Crowning Moment of Heartbreaking. Case in point: Right before Clara slams the door in Doc's face, she demands to know why he would make up such an elaborate lie about traveling to the future when a simple "I don't love you" would suffice. She slams the door... and cue Doc's big brown puppy-dog eyes filled with pain when he says to the shut door, "But that's not the truth!"
The Telltales Game
Surprisingly enough for this Troper, when Marty first meets with "Citizen Brown Universe" Biff in Episode 3, you find out that Biff is forced to be a good guy and follow all the rules or else. At first, you don't seem sorry for him as now he's not the evil bastard he was like in the past movies and previous episodes, looking to be a changed person for good. But you can tell that he regrets dearly being a Citizen Plus by the way he talks, especially when he gets to the part about giving up his many dogs, you can't help but feel sorry for him.
In Episode 3 it's hard to watch Citizen Brown struggle with what he's done. The road to Hell is paved with good intentions, indeed. Thank God for Doc's notebook...