The Tiny Tim Scene from the Ghost of Christmas Yet To Come. The Ghost of Christmas Yet To Come (who reveals himself to be Pete) takes Scrooge to the future where Tiny Tim, Bob Cratchit's youngest son dies. The scene where Mickey (as Bob) places Tim's crutch by his tombstone with tears in his eyes is beyond heart-wrenching. It's a difficult scene already, but damn it, Mickey should not look like that. A tearful Mickey is very hard to watch. But seeing his character utterly broken like this is almost unbearable. Without even a shred of humor, levity, or optimism, it may very well be the single saddest scene Mickey has ever taken part in.
Yet another reason — this is one of the few, if not the only, incarnations where Mickey and Minnie have kids. Stomach that for a moment.
The scene where Scrooge coldly rebuffs Isabelle, who in the years she has awaited his vow to marry her has become the greedy, thoughtless miser we know him as. Having bought for themselves a honeymoon cottage, she asks if he has made decision. His answer: He forecloses on her mortgage for being an hour late on her last payment. Devastated, Isabelle leaves the counting house in tears before angrily slamming the door on Scrooge, walking out of his life forever. To make matters worse, it was not until the Ghost of Christmas Past showed him this that Scrooge realized what he had thrown away, having been madly in love with her in his youth. He wakes back up in his bedroom, agonizing over his foolishness.
"Remember, Scrooge — you fashioned these memories yourself."
Made even worse when you realize Isabelle continued to hold out hope for him even when we see that greed has already taken Scrooge long ago; the hearts that shatter around her when he cuts her off really seal it.
The Disney story book version features Scrooge's reaction to his own fate, which beautifully shows the real lesson about the future ghost. Scrooge shouts "No! I didn't want my life to end this way!" The "this way" part is a small but effective method of showing the true reason why Scrooge was afraid of this future. He wasn't afraid of dying, it was the way he dies that scares him; as a bitter, greedy, hateful old man who nobody loved and nobody mourned.
In a meta example, this was the very last time Clarence Nash provided the voice of Donald Duck prior to his death in 1985. He has only a few lines, and you can hear the age in his voice.
Most of the cast has now passed away, with Hal Smith (Goofy/Jacob Marley) dying in 1994, Wayne Allwine (Mickey/Bob Crachit) in 2009, Eddie Caroll (Jiminy Cricket/Christmas Past) in 2010, and Alan Young (Scrooge) in 2016. The only three still alive are Will Ryan (Willie the Giant/Christmas Present and Pete/Christmas Future), Dick Billingsley (Tiny Tim), and Patricia Parris (Daisy Duck/Isabelle).