I once had plans to program my own monster-related RPG/simulation called Tenkai ("Celestial Monsters") when I was 12.
...At this point in the story, the narrator would usually describe how they abandoned something and went a completely different direction.
But not me. As you already know, I'm literally still working on it. XD
Of course, it's not really the same thing at all by now. Here's a brief overview of how it's changed over time.
Tenkai started life as something called "Aeromon". In the very, very, very beginning, it was a very thinly-veiled Pokémon imitator, that I believe was essentially born out of me creating what were basically "fakémon" but wanting to assign attributes to them that I knew Pokémon never had canonically.
In particular there was a creature called the "Crysterius" (crystal + mysterious :p) which was essentially a Starmie clone, but with waaaaay more arms to the point of being more of a spiky ball than a starfish and made out of translucent crystal. It had the ability to absorb things into it that then just kind of... floated around in stasis inside I think? But somehow it actually gained power from that, even though it wasn't digesting them. It was like... the more matter was inside it the more powerful it was, and it was kind of a portal to its own little pocket of space where all the things it sucked up lived.
Crysterius was probably my most interesting fakémon, and I kind of started to form its own plot around it, where Crysterii were floating all around the world absorbing things into their cores with tractor beams, up to and including trees. I'm not sure, but I think this in particular was the thing that inspired me to split my creature creation from Pokémon into Aeromon in the first place, just because this scenario would create a totally different kind of world from the Pokémon world. So, I had that plot thing. I figured out that if Crysterius cores were good for storing stuff, maybe they'd be a good alternative to a Poké Ball (I might say Monster Ball, but that was before I actually watched Japanese Pokémon, so, yeah), possibly even better because the full cores at least could store so much more. I even made up this neat little intro gif for if Aeromon were actually some sort of gameboy game or... something like that, which you can see below.
So what happened after that?
I just kind of forgot about the Crysterii and their little plot as I was expanding my creature roster. Don't ask me what happened there! In retrospect I think I didn't realise back then how awesome and weird an idea they actually were.
But anyway, I tried to develop the story. Not unlike I've seen some of my own friends of ages close to what I was then do today, I quickly decided I'd never be awesome enough to build anything as complicated as a game, or even as skill-requiring as a visual-type story for this (or at least not gather either of those skills quickly enough to be able to do either of those things before I scrapped the project), so I broke out the good old word processor and tried to novelise it. I think that was something of a bad decision, honestly; everything about the story was really rather visual, and a purely text format kind of took away what was cool about it, leaving only excessive thesaurus use and cringeworthy weeaboo-isms behind. I think I'm just generally really, really bad with text stories as a medium, to tell the truth, as it's oddly tiring for me to read them even though I can get through chapters upon chapters of dry biology and physics textbooks with great enthusiasm, and I've practically never gotten anywhere writing them either. Visual stories may take effort to progress, but in some ways that's kind of a quality filter for me, as it doesn't allow me to just let endless streams of substance-less words flow out of my fingers without a reality check as to whether I'll end up deleting them all later when I realise they're crap and don't convey the story I wanted to tell at all, and be back at square one. Over the years, I've come to the conclusion that text stories are not easier than visual stories, despite what you might be led to think, and thinking that will just make writing harder for you.
Anyway. By the time "Aeromon" had gotten to its novel phase, I'd realised the name Aeromon was already a Digimon name, and even though I didn't know anything about copyright at all at that age, I already knew more than enough to not want to deal with IP collision bullshit, so I changed the name to Adventures of Kurei (which amusingly enough abbreviated to AoK, and I joked that, well, now its name was AoK :p). It's interesting to note that ironically, in trying to pick a more "original" name, I literally just picked the name of some random Japanese-tutorial guy I was reading a page by (Clay/'Kurei') as the name for my protagonist, while Aeromon had been something I actually came up with off the top of my head. (Wait... no, actually, the protagonist wasn't actually named that. I just picked that for the title because it sounded a little bit like his actual name, but 'in Japanese'; I'm not sure I ever had any plans for anybody to call him that, to be honest. It's sometimes hard to explain the choices I made in trying to put together stories 7-9 years after the fact.)
In a short while, AoK began to evolve into a sort of monster notebook project. Now, I mean that very literally—there was literally a physical notebook that I think even had a table of contents, which I was literally creating entries for various creatures in. It was overall a little bit like what I'm doing with Stablehand/Tenkai, but a lot less intentionally planned that way; instead of the monsters really being specifically designed to fit into both stories or either of the stories being designed around the monsters I was honestly just kind of creating them and sending them off into limbo not really knowing or thinking about where they were supposed to go. :p
Now, compared with what I'm creating now, the creatures in this notebook were really a little plain. Many of them were just "take a creature out of mythology/regular animal and add a weird add-on, particularly an element or single new body part, that then becomes the theme". In this category were "Wulfangs", which was literally just a wolf pup with visible protruding fangs that then became one of two unicorn wolves and then some random oddly-Halloweenish designs (these guys were kind of the "let's see how many weird but yet obvious puns I can get away with" line to be honest: Wulfangs, Wulfantom, Wulfury, Wulfantasy... Wulfuego-hielo because I was obsessed with foreign dictionaries :p); a thing named for the Acropolis that was literally just one face of a Greek building with two pillars as legs because I had to have an example of a "Cement-type" creature (this came from me dreaming that my randomly-anthro Pidgeotto's status incorrectly claimed he was Cement-type); and Javuu, basically a hippogriff but with improved Ditto powers because I needed a name for it and Javuu from déjà vu was the first thing that came to mind. A small handful of others, maybe 2 or 3, were essentially Pokémon ripoffs that were supposed to be alternate evolutions but of course since the actual Pokémon were not going to be in it they had to be distinct to make sense; one was named Far-Flung and was able to wield "Psy powers", whatever that meant (one thing I do know is that "by the way, Psy is not the same as Psychic", as my somewhat underline-happy teenage self so helpfully pointed out for a friend :p). Others, like Blizzarisk and its other elemental forms, were halfway between these two categories, and yet others like Pythoria had almost no visible difference from real animals save possibly no real species of that particular type of animal having that specific colouration.
Blizzarisk is a pretty good place to pause for a moment, actually, because it shows one of the major things I was trying to develop for AoK. I think at that stage my favourite Pokémon ever was Eevee. I LOVED Eevee and the fact it had so many different evolutions, and just like everyone else, I made and tried to draw my own Eevees to fill in the gaps and everything. I was so obsessed with Eevee and its different type specialisations that I wanted to literally turn everything into Eevee. EVERYTHING.
There were exceptions, of course: some creatures like Wulfangs obviously were not subject to the Eevee treatment. Wulfangs I think either came from just being unsatisfied with Pokémon having only three stages, or wanting to emulate the evolution system in Telefang, where a small handful of Denjuu had like seven different stages split across different branches of a tree. There were a handful of things where I was trying really hard to give them different branches and "mod evos" the Telefang way even before I really knew how Telefang worked beyond what I'd read on Racieb's pages.
I was also trying really hard to make the rock-paper-scissors part of my elemental system be complicated and nuanced but I don't think I even had any idea what I was doing there because I didn't get very far on that.
Now, this kept sliding along chaotically until, guess what, I actually started learning to program and sprite! And then, for some reason, I had to start from scratch, because my AoK stuff just wasn't good enough or something. I think it may have been that I was planning to integrate a bunch of the AoK monsters back in later, but I just wanted to get my game working and establish its style and rules first.
In this stage of things, I had an almost completely different approach from what I'd been doing before. For one thing, it was now more based on Monster Farm than Pokémon and random fantasy stuff. For another, I had by that point entered one of the most gigantic weeaboo phases imaginable. A weeaboo phase so big, it was the size of Gojira, and not Godzilla. Everything had to be named in Japanese. Everything. And everything had to be inspired at least loosely by Japanese myth/tradition, if only actually related by name.
Accordingly, I called this new version of the project Tenkai. (This name was a combination of the kanji for heaven/sky (天) and monster (怪), that I then discovered sounded just like tenkai (天界), a word for heaven/paradise, so it was actually kind of a neat pun. I've stuck with that name because I still like it.)
In general, in Tenkai, the monsters were somewhat more pet-like than in AoK in that hunger, health, lifespan, and damage as distinct from fatigue were all things, and you could train them to do things like perform better at different statistics and learn new techniques by combining techniques they already had. A major part of the game as I remember was going to be just trying to figure out all the different things you could do with each one and make it learn and make it become. (In a couple ways, my current version of Tenkai is probably going to very much derive from the way Gojiraboo Tenkai was going to be structured, given that really, that central idea of potential and different ways to unlock it is kind of like the premise of Stablehand, and an idea I really like in general.)
It's also interesting to note that this version of Tenkai, much like AoK before it, also had variants, but instead of elemental variants they were regional, much like in Monster Farm 3. Each one was like a breed the region was known for, and I was planning a system where you could breed monsters to get other variants that were sometimes combinations of existing breeds but other times "secret" creatures. I think I could have made that much cooler if it'd occurred to me to actually learn something about genetics and patterns of inheritance and separated this out into specific traits, rather than just mashing up appearances. :p
So, after that, about three years ago and one year after I let that version of Tenkai slide into the never-going-to-be-finished pile (six years, I think, since Aeromon began), I came back and rebooted Tenkai yet again, seeking to have more unusual and less overtly Japanesey stuff, and that's where Stähe (Stähe was actually revamped from the Aeromon stage), Kuryne (sort of a revamp of the dogs from the weaboo stage), Ajan, and similar guys came in. This time I was going to take yet another a new approach to variants, by focusing on habitat types and theming mons and their abilities around their habitat type, with the variants being themed around other habitat types. A major focus of this stage was making mons "realistic"—by this I didn't really mean "exactly like real animals" or even "immediately plausible in the real world" as much as just, you should be able to draw/model them in a completely photorealistic way, consistent with other animals, and no part of them should be so cartoon-stylised you can't figure out how it would "really" look. Accordingly, Stähe for instance lost its featherhands and got bulky pawhands instead.
Now, nine years after Aeromon began, I'm rebooting Tenkai one more time, this time as a libre monsterpet game. As I've already described, it will likely be a spinoff of Stablehand, featuring things like hexarts, leijonœrns, and the elusive "Heavenscratch" (a cœlailurus basically, except real), along with some new creatures designed specifically to be unusual and slightly unearthly, such as the Sonata snake. The variant thing is still alive, but I'm thinking of doing it mainly as different Stablehand attributes rather than elements or habitats, and having the monsters actually able to freely shift between the different attribute-forms; habitat types miiiiight maybe come into play too though, I don't know.
Anyway, stay tuned for more updates on "Heavenscratch Beastquest Tenkai", literally nine years in the making.