Sweeney Todd: The Demon Barber of Fleet Street (film)/WMG

The film version's cast is the commedia dell'arte troupe from hell.
Sweeney Todd and Mrs. Lovett are the zanni gone horribly wrong- in a love hate relationship, both scheming their heads off with a private agenda, and both supposedly in positions of service- Todd obviously as a barber, Lovett a... humanitarian piemaker but a piemaker nonetheless. Anthony and Johanna are obviously the innamorati. Judge Turpin and Beadle Bamford are the vecchi, attempting to prevent their marriage by any means necessary- except Turpin's, well, a rapist. And by extrapolation, Pirelli gets to be Il Capitano.
 * But there are characters that don't fit the mould... I'd say the film merely shares archetypes with the commedia dell'arte tradition, and is not quite inspired by it... then again, you have some cool points.
 * Please explain! I want to hear what doesn't fit!

The film's Toby grows up to be Jack the Ripper.
Think about it: he's an abused boy from the moment we see him, up until Sweeney kills Signor Pirelli and Mrs. Lovett basically adopts him. Afterwards, she treats him lovingly like the mother he's been portrayed to never have had. At the end, Mrs. Lovett locks him in the cellar with the intent to kill him for knowing too much, and then he watches Sweeney throw her into the furnace. It's enough to drive him insane. Now, couple this with the fact that the story takes place in roughly the same time-frame that would allow Toby to grow up into this persona and the fact that, in the late 19th century barbers were still the place to go for minor surgical procedures where Toby could have watched and studied Sweeney in his work, plus a little hatred of women because of Mrs. Lovett's betrayal and you have a perfect formula for a serial killer. Why only prostitutes? They were usually without family and were always out on the streets alone at night. Easy, forgettable targets.
 * DUDE. THAT IS COOL.
 * Johnny Depp being in From Hell (a Jack the Ripper movie costarring Hagrid) makes this even cooler.
 * Except From Hell totally sucked. I wanted Johnny to be Jack, not some junkie! But this theory is way too cool to be an epiliptic tree. It makes me want to write really gory fanfiction.
 * Y'know what'd make this a hat trick of cool? What if the Ripper murders were done using Sweeney Todd's razors? He'd have five more murders by proxy! Well, if he really had existed...
 * Well, you gotta do something with them... (In this troper's personal continuity, Johanna kills Jack the Ripper. With her dad's razors, of course. Mostly spawned by the deliberate misinterpretation of fanart.)
 * Sweeney Todd did exist.
 * Or not. Anything is possible but research into crimes at the Old Bailey and other researches by historians have found no clue that there was an actual murderer named Sweeney Todd or anyone who dispatched their victims in this way. However, there were many legends and tales about cannibalistic meat pie vendors and gruesome murderers, any of these could have been based on or inspired by some crime that does not come down to us. A mad serial-killing butcher killing people with a straight edge razor could have existed in the first part of the 1800s. Sweeney Todd (as a named person living in the 1800s) most probably did not exist.
 * Also on the Toby-as-Ripper front-- if you go with one of the productions with a sturdy, matronly older Lovett (as opposed to HBC's Marla!Lovett) there's a bit of resonance with the majority of the victims the Ripper chose, which were middle-aged, slightly overweight women down on their luck.
 * Also, somewhere between the events of Sweeney Todd and Toby's killings as Jack the Ripper, Toby will change his name to Sebastian for unknown reasons (maybe as a result of his traumatization).

Tim Burton's version is a dark and twisted sequel to Sleepy Hollow
After returning from Australia and believing Katrina dead, his daughter captured, and his manservant (Masbeth/Play!Toby or Movie!Anthony) missing, Ichabod changes his name and takes on the Headless Horseman's persona (+head, -horse). Katrina and Masbeth suffered from traumatic amnesia in his absence.

There will be a Hollywood sequel to the film that will be a huge source of discontinuity
It will be called: "Sweeney Todd 2: Turpin's Revenge". Turpin somehow survived. Anthony and Joanna will hit a rocky patch in their relationship when Anthony is tempted by the hot new female lead, a perky Action Girl in skimpy clothing. The plot will focus on two villains: Turpin and Toby, who is now a murderer as bad as Todd used to be. Todd will have been returned to life as a dark antihero, and his only chance to escape an eternity in hell is to defeat Turpin once and for all. The climax will be an epic razor-blade duel between Todd and Turpin on top of Big Ben (which, anachronistically, will be in London), interspersed with a tense chase scene as Anthony, Joanna and the new female lead try to apprehend Toby, who is fleeing through the sewers after having killed Anthony's long-lost twin brother. At the end, Todd kills Turpin and is allowed entry to heaven, Anthony learns that Joanna is his one true love, and the new action girl gets Toby to change his evil ways. At the end of the film, they team up, leaving it open for a third film or an animated series in which They Fight Crime.
 * I threw up in my mouth a little.
 * I laughed. Heartily.
 * If that happens, I'll die more than a little bit inside.

Movieverse Johanna becomes a full-time Sweet Polly Oliver.
Whether Anthony goes back to sea and she follows, or the two merely hide from the Lawr under this guise is debatable. At least the 2001 concert cast has her dressed as a sailor singing that she'll go to sea with him.

Movie version: Bellatrix Lestrange and Peter Pettigrew have stolen a time turner in order to have some fun and cause mischief in the nineteenth century.

 * Bellatrix shares her fashion sense with Mrs. Lovett, as well as having a crush on a ruthless serial killer. Also you can't deny that baking pies out of human meat would not be exactly that far out of character for our lovely friend Bella...
 * Meanwhile, Wormtail enjoys himself by being the right hand of an evil and powerful man.
 * Judge Turpin on the other hand, just happens to look like Severus Snape by mere coincidence.
 * Not to mention that young Gellert Grindelwald seduces and then runs off with Snape's ancestor's ward and intended wife.

Alternative to above: They're actually related to the characters in the movie
They're all the grandchildren of identical twins. Also, Johanna had a son named Willy, who moved away, built a candy factory, and changed his last name to a silly, alliterative word. He then had a son who took the name and factory in a new (trippier) direction and looked like Benjamen Barker.

The Mrs. Lovett seen in the film was actually a fangirl of Sweeney's.
She found her way into the movie somehow, probably by killing the real Mrs. Lovett -- who would've immediately turned Todd back over to the judge.

Toby is the son of Judge Turpin and Lucy.
We see in the movie that Lucy was drugged and raped by Judge Turpin at a masquerade ball. What if, Lucy became pregnant following the rape. She gave birth to Toby and then drank the poison, going insane. Johanna is adopted by Turpin, and Toby falls through the cracks, and with no one to take care of him, ends up in an orphanage. After several years, he is hired as Pirelli's assistant.
 * Well that's just silly, because Mrs. Lovett would have noticed her get pregnant, and Mrs. Lovett would have put that in the story she told Sweeney wait... unless...

Mrs. Lovett will have a descendant who becomes a psychologist and falls in love with a madman...
...only instead of a Mr. T, she'll fall for a Mistah J.
 * Another descendant of hers (Lovett was, being a Muggle, erased from the family tree) falls in love with Lord Voldemort.