So, I was deciding on a plot which involves the character "transforming " into another creature (in this case,a black fox).I was trying to put him (transformed version) at the first chapter, and let the plot develop in a descending order, but I am not so sure about how to put this. My idea: chapter 1: (transformed version linking back to the start of the story) C2: story(untransformed) C3-8:untransformed C9: transformed, linking back to C1 C10:ending (?)
It all depends on the payoff. If we know from the opening chapter that the MC will eventually become a fox, there won't be much tension in the transformation because we'll already know how it ends. So when strange things happen to the MC you won't be able to sell the whole "My God, what's happening to me?" gag to the reader because everyone will know he's turning into a fox. If you choose to got that route you'll need a different reveal/payoff and another reason for us to want to continue reading. It can be done, but it's really hard. The movie Memento is probably the best example of reverse order plot, but the gag in that story is the audience has no idea of the beginning until they reach the end. But what you're describing doesn't really do that (I think). You're not going 5-4-3-2-1 in chronology like Memento, you're going 5-1-2-3-4 with the plot points, which basically means you're giving away the ending and then writing the rest in order. I could be wrong about that, but that's the way I'm interpreting your post.
This could work and here's how: The transformation happens and the character is as clueless as the reader. The character then blacks out and when he/she comes too they are human again. They have only nightmarish memories of what happen during the transformation. Now, they're backtracking their last few days to find out what has happen to them before it happens again and what happen during the transformation. Think 'Hang Over' with werewolves.
I probably will let the MC (Transformed)@ Chapter 1 says the story before the transformation. Something like: "Why has this happened ?Oh , I remember, it all started at..." Will that work?
People usually move a later part of the story to the first chapter when they're afraid their real first chapter (untransformed) isn't interesting enough to grab a reader's attention. The solution is not to put events in unchronological order, but to make your real first chapter interesting. Or, possibly, to forget the idiotic advice articles that insist your first chapter must contain 25 dragons and a car chase because readers only have a four-second attention span. There are good reasons to write events out of sequence, but most of the time the best course of action is to start as close to the beginning of your story as possible. That means as close to the inciting incident as you can. The further away from the inciting incident you begin, the more you risk including irrelevant details.
Might work. Might not. Hard to say anything about an idea in a vacuum. It's all in the execution. In general though I would dissuade you from using "It all started when..." because that's kind of implied in all stories. It always starts when we opened the cover and read page one. And again, you're giving away the "ending," so you'll need a deft touch to make the rest of the story compelling, which can be done, but it's really, really hard.
Some authors are really good at foreshadowing, but also the type of foreshadowing that includes things like saying so-and-so was living the last day of their life, which implies that by the end of the day, they'll be dead. They may even say how they died ("[so-and-so] would end the day with their brains leaking on the pavement, but for now they were getting brain-freeze by eating their ice cream too fast" -- something like that), but they do this for a reason; the tension doesn't have to do with wondering if they will die, but why and how. It can work as a good teaser to read the rest of the story or the chapter, throwing out that awesome tidbit and then backing up. You can do the same with your story, but my suggestion is to look up some writers who have done similar things to what you're suggesting, and then see how they did it and why it worked (not saying to copy them, only to help gain an understanding). If I can think of some stories that fit this example, I'll come back later and update this post.
Did I mentioned that nobody will know the fox is the MC in the first character? I never mentioned the MC's name in the first chapter, though.
Plot told in deconstructive order is a slippery slope. If you pull it off, great, but you run the risk of letting the reader get ahead of you. Balance the story from beginning to end and don't use up all of your creative equity in the first third of the narrative. Maybe alternate the sequence/order of the transformation? Just a thought.