The Red Jinn in Oz, by Mildred L. Palmer - I'd heard about this book, which was written some time ago, but I'm not sure exactly when. I think it might have been in the fifties or so. Anyway, it remained unpublished for years, but I did a Google search on a whim a week or so ago, and it's actually available as a free download on Lulu. The copyright date on it is 2007, but I don't know how long it's been up there. Oddly, it doesn't appear in Lulu searches, supposedly because it's not "interesting content." Wait, Lulu, who decides that? Anyway, this was a traditional and quite fun Oz story, largely following up on The Purple Prince of Oz. In that book, Faleero took over Pumperdink, and Ozma punished her by turning her into a raven. In this book, she seeks revenge by transforming Ozma and taking her place, while her cohorts take the forms of Glinda, the Wizard of Oz, and Jellia Jamb. It's sort of like Magical Mimics in this respect, but not enough to seem repetitive. Besides, I'm not sure when this was written relative to Magical Mimics. Unfortunately for Faleero, she has trouble controlling her temper, and Dorothy soon realizes something is amiss. She and the Cowardly Lion seek the help of the Red Jinn, and the three of them return to set things to rights, after a stop in the sky kingdom of Cumuland to restore the rightful ruler. Everyone is in character, and it very much feels like an old-school Oz book, particularly one of Ruth Plumly Thompson's (not surprisingly, since it follows up on one of her plots). The bit about Guph having conquered the Nome Kingdom from Kaliko was never really developed, but maybe that's something that can be expanded on in a future story.
An interesting thing about Red Jinn is that Dorothy and the Cowardly Lion use the Nome King's tunnel under the Deadly Desert to get from Oz to Ev. The tunnel was also used as a plot device in Shaggy Man, but I don't know that Palmer had read that one. Regardless, it seems like both of them missed a relevant passage from Chapter 29 of Emerald City: "That day she watched her Magic Picture, and when it showed her that all the Nomes had returned through the tunnel to their underground caverns, Ozma used the Magic Belt to close up the tunnel, so that the earth underneath the desert sands became as solid as it was before the Nomes began to dig." So why would it still be intact several decades later? One possibility is that something went wrong, and the tunnel was never sealed, except for the two ends. If we want to accept both this passage and the plots that involve the tunnel, however, there must have been some kind of restoration. One idea that comes to mind is the idea in the Discworld books that it's easier to magically change someone or something if they can remember having had that form before. In Witches Abroad, the witches turn Nanny Ogg's cat Greebo into a human, and although he's later changed back, we learn in later books that he can take human form on his own in certain situations. So if that sort of magic is possible in Oz and its surrounding fairylands, perhaps the tunnel could be restored without too much trouble because it can remember having been there before. Or perhaps it was some sort of regression magic, which is something I wrote about in a multi-authored story called "The Ruby Ring of Oz" on the old Oz Club forums. Someone else had brought the Shaggy Man's brother back to the Metal Forest, and I explained this by introducing a wizard who could cast spells to restore someone's state and location from an earlier time. Neither of these explanations has any real basis in what we know about Oz, but hey, they're always possible, right?