When Dorothy arrives in Oz, she appears on the edge of the Deadly Desert, which abruptly segues into a lush forest area. Geography freaks might be quick to point out this makes no sense, which would be true... with any other desert. Eventually, you find out how the desert got its name when a Wheeler unintentionally falls into it from a ridge. He promptly morphs into sand after a short, panicked struggle. Now think how a desert like that could possibly expand its boundaries to get so huge...
The books confirmed this as the major reason why Oz has rarely been invaded. Without flight capability, massive digging efforts, powerful magic or acts of nature, it's nearly impossible to cross the Deadly Desert.
That movie was stuffed with fridge horror, particularly of the Freeze-By-Time variety. For example, Jack Pumpkinhead's... head. He asked Dorothy to check him at the beginning of the movie for signs of spoiling. Sure, he was fine right then. But how long is it going to be before rot sets in?
In the books, Jack ends up keeping a pumpkin patch where he grows replacement heads, so apparently getting a replacement head isn't a big deal for him.
That leads to the question, when Jack throws his old head away and puts on a new one, is Jack himself being thrown away to rot, with a new person taking his place?
He appears to be the same old Jack regardless of head, retaining the same personality and memories. Of course, there's an incident in the books where Jack attributes being cleverer than usual to the current pumpkin having smarter seeds.
Then there's the girl from the mental hospital whom Dorothy later recognizes as Ozma. Since the movies played it so that Dorothy was only dreaming her trips to Oz, with every Oz character being inspired by someone she knew in real life, that means the girl really did drown in the river after she helped Dorothy escape.
When Dorothy meets Ozma, she says "I thought you had drowned". Considering the girl in the hospital appears and disappears at will, it was almost definitely her. This film doesn't portray Oz as a dream - Dorothy's old house is still there when she goes back.
It's a children's movie and Dorothy narrowly escaped being given primitive shock therapy.Or did she?
She did. Whether or not Oz was real, the storm, her escape, and the raiding and arresting of the hospital staff definitely was.
Mombi stealing the dancing girls' heads is creepy enough. But even though they're turned to stone, she likely beheaded them before she petrified them.
Dorothy may have managed to escape electroshock therapy, but there are those "damaged" patients in the cellar that Ozma talked about. Auntie Em says that everyone but the doctor was rescued from the storm, but can we really be so sure they thought to look in the cellar? And even if they did, depending on how much the shock therapy messed with their minds, those patients may not be that much better off...
The head-nurse being taken away by the police at the end of the movie would suggest they found the patients because why would she have been arrested otherwise? Their physical and mental states, however, are still another matter.
Even though Dorothy escaped the doctor's and knows Oz is real, she still can't talk about it to anyone.
There's a popular fan theory that Wizard of Oz is a metaphor for coming out as homosexual. Given this, the most logical explanation for this movie is that it's a metaphor for being out in a homophobic society... which they try to cure... with shock therapy.
As powerful as he is, why would the Nome King want to become human?
Solely to be able to wear the shoes, because the shoes are even more powerful.
Because he'd still be the Nome King and able to command his people, but he also wouldn't be able to be killed by a plate of scrambled eggs anymore.
How was it possible for Dorothy to get to the Emerald City in what seemed like a few hours when her original journey took days?
Maybe because she didn't stop to rest or get harassed by apple trees this time?
Murch took delight in playing around with the "Oz is a dream reflection of Dorothy's psyche" explanation from the MGM film. In a dream locations are as close or as far as the dream's own internal illogical logic dictates.
All mirrors may serve as a gateway into Oz. Mombi thought she had trapped Ozma within a mirror but instead pushed her into Dorothy's Kansas. Upon arriving, Ozma would have been seen as mentally ill and placed into the hospital. Once Dorothy arrived, Ozma escaped with her and ran directly to the river, the surface of which could also be used as a mirror (which is how Dorothy and Billina arrived in Oz). When Dorothy disposed of the Nome King and Mombi, she then drew Ozma through the "mirror" of the river and back into Oz. Thus Ozma would disappear entirely from our world and give the impression that she had drown. The only real question is why she didn't just jump in the river and return to Oz with Dorothy.