As per request, here's my post on Pigasus, cross-posted from here.
When Ruth Plumly Thompson introduced a flying pig into the Oz series, she wasn't being entirely original. The expression "when pigs fly" apparently dates back to an old Scottish proverb, and I've seen many images of winged pigs that have no known connection to Thompson or Oz. The Kids in the Hall even had a flying pig. I'm not sure whether Thompson was the first to refer to such a swine as Pigasus, but that was also the name of the pig that served as John Steinbeck's personal stamp, as well as the Yippies' 1968 presidential candidate (although that pig didn't have any wings). Pirates in Oz, the first Oz book to feature Pigasus, was published in 1931, but I know of no indication that the Yippies read it.
Anyway, though, while maybe not a unique creation, Pigasus is an Oz character whom I quite like. Thompson must have liked him as well, as he actually has a starring role in two of her books, unlike so many of her original characters who were pushed into the background after one significant part. Pigasus is a creation of the Red Jinn, although it's never entirely clear what that means. Did Jinnicky magically modify an existing pig? Was Pigasus the result of selective breeding? I suppose the Wizard of Ev doesn't want to give away all of his secrets. Regardless, Jinnicky gave the pig as a gift to the Duke of Dork. When Captain Salt's crew invaded the Duke's castle boat, Peter Brown traded a Bananny Goat for the flying swine, and Pigasus became part of the reluctant pirate crew. After flying Peter to the Emerald City in an attempt to thwart Ruggedo's latest invasion plan, Pigasus decides to remain there.
In addition to flying, Pigasus also has the magic power to make anyone riding him speak in simple rhyming verses. (Incidentally, an Oziana story by John Bell has the normally rhyming Scraps riding Pigasus and speaking in abstract free verse instead.) And while this ability isn't mentioned in Pirates, Wishing Horse establishes that he can also read the mind of anyone on his back. This power comes in handy when Dorothy is the only one who remembers Ozma after King Skamperoo's enchantment, and the two of them set out together to break the king's spell and restore their rightful ruler.
For what it's worth, I dressed up as Pigasus for the 1996 Munchkin Convention and the following Halloween, but I don't have any pictures handy.