Later authors introduce a few more people in the category, starting with Bill the Weathercock. There's no reason to discuss him again in this post, so I'll move on to:
Humpy - Yes, that's the character's name, and it's a quite unfortunate one given how the language has evolved. He's a motion picture dummy from the early days of Hollywood film-making, and his story is that Dorothy found herself on Wish Way, and inadvertently wished herself to California and the dummy to life. She named him Humpy because he was "dreadfully humpy in spots," and took him back to Oz. It turned out that the dummy, who had most recently been a double for a king, bore a close resemblance to Ozma's father Pastoria, and his serial number was the formula necessary to restore the former King of Oz. As with a lot of seeming coincidences in the Oz books, it's never revealed whether there's any reason behind this. His personality owes a lot to his experiences in the movies, and he ends up working at a tailor shop. Speaking of dummies, Thompson apparently considered using a dressmaker's dummy named Judy as a character in a proposed sequel to Ozoplaning, but that ended up never being written.
Benny - Dan, an Irish second-hand store owner in Boston, somehow ended up with a suit with a book of magic in one of the pockets. When he read some passages from it out loud in front of a park statue of a public benefactor, it brought the statue to life. When writing this episode, Thompson seems to have been inspired by John Dough, and possibly "The Dummy That Lived" as well, as his first order of business is accessorizing with a top hat and umbrella. He ends up stumbling into a hole in the road blown by construction workers, and lands near the Emerald City. So Oz is underneath Boston? Since this doesn't fit with anything in any other book, there must be more to that hole than we see in the story. Honestly, considering how quickly most of these characters end up in fairyland, perhaps there's some kind of magic involved in removing anomalies like these from the mundane world. Anyway, the statue meets the Scarecrow, who names him Benny, which is short for "public benefactor." He initially wants the Wizard of Oz to change him into a flesh-and-blood person, but he goes on to decide otherwise.
The Collapsible Kite - Perhaps the kite doesn't exactly count, as there's no indication in Hidden Valley that it's alive while in the United States, but it DOES come from there. In fact, Jam builds it with instructions from a magazine, and it takes him to Oz. When he comes across an island of live kites who were stolen from Winkie children by the Wicked Witch of the West, Jam draws a face on his own kite, and it begins talking as well. The Collapsible Kite remains in the Winkie Country while Jam returns with the Tin Woodman to the Hidden Valley, so it's never really developed as a character. The Wizard does enchant the kite so that it can return to Oz whenever Jam chooses, but we never see the results of this. Rachel Cosgrove didn't use Jam in her later Oz stories, and while he does appear in a significant role in Blue Emperor, he gets back to Oz by wishing pill rather than Collapsible Kite.
Merry Go Round - Robin Brown from Oregon travels to Oz when he grabs the brass ring on a carousel, and the scarlet-painted horse he was riding comes with him. In fact, the horse comes to life, and proves to be a friendly and loyal companion to Robin, although she initially has trouble walking in a straight line instead of circles. Like Benny, she wants to be turned into flesh and blood, but later changes her mind.