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.
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.