Well, I'm completely stumped as to who the culprit might be this time. I think the only tangible clue besides the method of transformation is the symbol on the book's cover.

It almost looked like an upside-down spade from a deck of playing cards, but was comprised of multiple colors, at the center there was a brown anchor shape which at the bottom had a yellow-orange arrowhead shaped tip. Then the entire thing had a white border.

...doesn't really remind me of anything.

I mean, it vaguely reminds me of my coloration. I seriously doubt that's actually the meaning, though.

The coloration reminds me in a way of Kickaha, which combined with the playful nature of this transformation makes me think he's the foxyote behind this book, somehow.

I freely admit to being behind this. Naturally, I will freely admit to being behind a quality prank whether or not I was actually involved in or even aware of the aforementioned prank.

Wait a second.
https://www.furaffinity.net/view/38517217/
Kickaha lost a magical book. And went looking for it in a magical shop specializing in transformation.
And then, when I commented, Calex did not deny said book being linked to the Thirteen Tales, despite the story not being part of it.

Yeah, Kickaha is my official guess for having TFed me. In which case, I humbly request more TF books, though preferably with slightly more comprehensible content this time around.

You're just convincing me that it wasn't my fault. I mean, look at the testimony. My book disappears from my possession. Later on, a book -- let's assume that it's my book -- baps you on the head. And yet later on, the book disappears again. How can we explain this? Clearly the evidence points to one thing: an unknown book-stealing malefactor.

But then why would this peculiar literary burglar steal a book from a magical foxyote, leave it in a library, and then come steal it again?

Also, how didn't said literary burglar get transformed? Say, into a cat, thus becoming a true cat burglar? Surely, if one steals a magical book from a karmic trickster, they would get karmically transformed, most likely in a way that is as awful a pun as possible? And if they did get transformed, into a feline for the sake of argument, how would the book have ended up in the library in the first place?

And, even ignoring all of that, it was surely Kickaha who brought the book back out of the library. Only a magical trickster could manage to concoct a scheme to remove a book from a library without the librarians noticing. And surely, only one who knew the magical properties of the book would even bother to take it out of the library. What is more, he must have known about its magical properties beforehand, so as not to read it before removing it from the library, thus rendering himself incapable of removing it. Only Kickaha would fit that description.

And, the coup-de-gras that proves all of this beyond a shadow of a doubt - first you claimed responsibility, stating "Naturally, I will freely admit to being behind a quality prank whether or not I was actually involved in or even aware of the aforementioned prank." Then, you went back on that statement by denying responsibility. The only logical way to explain this sudden change of tone is panic at being called out after attempting to brush off the suspicions with a joke.

Or maybe all of this is wrong. I am part dog, so it's not an impossibility that I'm barking up the wrong tree.

(Also, I spent like half an hour writing that comment. Somebody please save me.)

That's a lovely tale, and I wouldn't dream of disabusing you of it.

...You know what, I just looked up Kickaha's ref sheet, and the symbol on his back just about matches the description of the symbol on the book. We have our suspect!

I do love becoming the object of a library pseudo-cargo cult. It's always a pleasure.

More snacks for the winged raccoon god! May the library forever stay in an organized state.

"Ye ministers of the land of silence and reading, hearken to my word. Thou shalt gather four cinnamon buns, two granola bars, and one assortment of weird candy from the corner store, and thou shalt bring it to the library, and thou shalt place it in the bowl. And then the Almighty Winged Raccoon shall return, and he shall organize all thy books. Only beware, that thou shalt obey the notes left on the librarian desk requesting specific foods and specific books not currently in the library's possession, so that the Blessed Raccoon of Flight and Book Organization shall never again abandon thy domain." - The Book of Eshel, 3:31

Kickaha, was this you? A mischievous foxyote with a magical book, with a symbol and coloration to match. Silly of you to leave such a magic book around now, imagine who could find it! (Although I must admit, was not expecting him to transform back into his normal form!)