There is a layer of subtle terror in Zemeckis's depiction of the Ghost of Christmas Future as an incorporeal shadow. With this spirit, Scrooge has no companion to serve as a guide or confidant to share his thoughts. In the beginning, when Scrooge talks to the charity men, he says he wishes to be left alone — and now he truly is alone.
This also explains why this ghost is crueler than in other adaptations; being Scrooge's shadow self, it would embody all the worst aspects of him.
Marley being stuck as a spirit gains a new explanation in this version. At the funeral scene, the first thing Scrooge does is steal the coins from Jacob Marley's eyes. The custom of putting coins on the eyes of the dead stemmed from a superstition that unless blinded, the dead could open their eyes and seek out others to join them in death, but an even older version of the custom dates back to Greek Mythology: When your soul entered the afterlife, you would be ferried across the River Styx by Charon, the ferryman, who required payment. Two coins were left with the bodies so that they could be used to pay Charon. Scrooge stole Marley's coins, thus Marley can't pay his way, so he is Barred from the Afterlife.
We see Ignorance and Want grown to adulthood. Ignorance seems to spend his life in and out of jail, while Want, a girl, possibly goes down another path of ill-repute. The Brilliance comes when Scrooge is dealing with the Ghost of Christmas Yet To Come and sees the two people picking through his belongings once he's dead. They look a lot like Ignorance and Want.
Want also gets put in a straitjacket, suggesting a mental asylum. Some venereal diseases—syphilis, particularly—have that effect on the brain and, by extension, the mind.
Scrooge's heartfelt and effusive thanks to the Charity Solicitor was partially to Jacob Marley.
Why was Jim Carrey credited for the role of Christmas Yet to Come who never actually spoke at any point in the movie? Beyond the fact that he did the motion capture performance for it, we are not supposed to know what the future will tell us so the most we can only do is guess or interpret before or once it happens. And that is what Scrooge did. He interpreted the Ghost's thoughts projected into his mind for us. Without him, we have to guess or interpret what the Ghost is trying to show, tell or do to Scrooge.
If you look very closely in Scrooge's counting house, you will see many cash boxes and ledgers opposite Scrooge's desk. All those items actually sum up Marley's threat to Scrooge that his chains are ponderous. In other words, if Scrooge died an unchanged man, all those cash boxes and ledgers would be included in his much larger chains than Marley's.
Many have thought it strange that Scrooge bought the prize turkey, only to send it off for someone else, most likely the butcher and the boy's family. However, some have seen it as one big plan by Scrooge to mess with Bob in a joyful way. The prize turkey is huge, no way one family could it eat, so more likely, the family who got the turkey, even if it was Bob's family, invited more people to eat it with them, which led to more people showing up, and that led to a party of sort. Bob did say he was late because he was "very merry" last night. Scrooge spent a good penny on the turkey to make sure Bob's family was fed and he could make his decision to him much more joyous.
The principal performers who provide motion capture for two (or more) roles play thematically connected or contrasted characters.
Gary Oldman plays both Jacob Marley, Scrooge's corrupt original partner, and Bob Cratchit, Scrooge's suffering but kind-hearted clerk who is promoted to partner at the end after Scrooge's redeeming experiences via the ghosts.
Robin Wright plays both Scrooge's sister Fan and his lost love Belle — the two most important women he ever knew and both of whom he lost under, in different ways, tragic circumstances.
Bob Hoskins plays the jolly Mr. Fezziwig in the Christmas Past flashback, but in the Christmas Yet-to-Come flash-forward, he's the repulsive fence Old Joe.
And of course, given that Scrooge's experiences with the three Christmas ghosts are informed by the life he's led, it makes sense that Jim Carrey would play all four characters.
Out of the three spirits, the Ghost of Christmas Past looks the most like Jim Carrey. Since young Scrooge also resembles Carrey (albeit with a larger chin), you could interpret this as the Ghost bearing the face of Scrooge's past self.
Want gets put in a straightjacket. Now consider how awful asylums could be in those days. Even if the doctors wanted to help, they didn't necessarily know how, and things there too often went very badly.
