All-Creature is a term I made up – and will possibly revise – to refer to a very specific…thing that happens in fiction.

Remember the hyphen!

An all-creature is a creature in fiction which is versatile enough that it absorbs other creatures into itself – or, at the very least, renders them redundant.

That may be a little hard to understand, so let’s use an example: the zombie.
Zombies are probably the best example of an all-creature because its effect on fiction is obvious.
Since the zombie has been introduced, it just keep re-appearing in fiction. It appears in many different shapes and forms, but all of them are identifiable as zombies. You don’t even have to call them zombies and they’ll be identified as such.
This is because the ‘core’ of what a zombie is is quite versatile: it’s mindless, often in crowds, cannibalistic, human(oid) and dead. Everything else is up to interpretation. Slow or fast? Can be either. Magical abilities? Why not?
The high variety of zombies often puts creators into an awkward situation, where they have to explain why there’s a variety of zombies (or they otherwise feel the need to include a variety). Or they end up adding varieties without thinking it thru too much.
Left 4 Dead is a great example. Besides standard ‘infected’ who are fairly generic, you have ‘special infected’ who posses special abilities that make them more dangerous.
Now, where does the “absorb other creatures” part come in? Well, I’ll use an unusual example from Resident Evil: the Tyrant.
The Tyrant is basically a folkloric golem. Golems are an artificial person (usually made of clay), which follow orders, are single-minded and are otherwise quite dim. The Tyrant basically fits all of that: they’re an artificial person, they are made to follow orders, they’re single minded and quite dim. Both of them are also powerful and consequently dangerous. Now, am I saying the Tyrant was based on the Golem? No. I’m actually pointing out that the Tyrant – basically a relative of the zombie in-universe – has rendered the Golem unnecessary. If someone wanted to add a Golem into Resident Evil (for whatever reason), they’d run into the issue of the Golem’s narrative/worldbuilding role already being fulfilled by the Tyrant.

This is the key issue of the all-creature: their core traits make them versatile enough that they can take the role of many other creatures and, thus, theoretically reduce the number of distinct creatures that an author can include.
This actually leads into a second issue, which is what to do about speciation.

Because an all-creature is versatile, it may become expected among the writers and audience to see…well, multiple types at once. Like how you see fiction include slow and fast zombies at the same time. Thus comes speciation.
Since you can’t (usually) include all given traits in a single creature – because they contradict, have fun having a vampire who can walk out in daylight while being susceptible to it – you start splitting them up. And that may end up going out of control, leading to more overlap with other creatures…or you simply losing track of all the creatures you’ve created.

Different settings and writers deal with these differently. Though I think it’s notable that this also happens in mythology and folklore, just that it isn’t as noticeable. How many creatures have been described as ‘vampire-like’?

The issue with an all-creature is that there’s a very high chance it will overshadow other creatures you attempt to introduce into whatever it is you’re making…so how do you solve it? Well…

This is the solution favored by Resident Evil and Left 4 Dead.

Basically, you deal with issues of speciation and overshadowing by just ignoring everything except the one or two creatures you’re focusing on. So in Resident Evil, everything goes back to the T-virus (or relatives) and Left 4 Dead just has The Infection™. So everything is a zombie, basically.

This is probably the best approach if you don’t need other creatures.

This is the solution that is favored by the likes of Minecraft, World of Darkness and Chronicles of Darkness.

The solution to the creature overshadowing other creatures is to just…let them absorb those other creatures, or just ignore the others.
So most vampire-like creatures are just weird vampires or “not quite vampires lol”. Minecraft does this with the zombie, both Vampire games do this with vampires…and CoD goes a step further with all kinds of other stuff like ghosts and shapeshifters.

The major flaws are that some creatures are not as easy to absorb as they may at first appear. Or you might end up eliminating uniqueness/nuance in the process.

This is the solution seemingly favored by most writers.

The way you solve this problem is quite simple: you just avoid speciation entirely and strictly define what the all-creature problem children are. So, for example, what a vampire can or can’t do is so strictly defined that there’s only one possible type of vampire.

I think that this approach is theoretically solid, but practically hard to actually pull off.
First of all, just because you have just one type of elf that is explicitly called an ‘elf’ doesn’t mean you won’t accidentally add another elf-like creature anyway.
Second, even the strictly defined creature may end up overshadowing the other creatures anyway. A concrete example of this is not something I can easily point to.

This doesn’t just list all-creatures, but also lists some which don’t count, but which could count…maybe. Or I list them just to dismiss them.

Elves are, besides zombies, probably the principle example of all-creatures. Since Tolkien, elves have mostly existed in three major forms: High, Wood, Dark…though people have come up with many other kinds of elf, or remixed them into who knows what.

They also ended up absorbing other fantasy creatures, especially in the popular exception. It’s difficult to differentiate Fey from Elves, for example.

And as is often the case with all-creatures: they end up rendering other fantasy races redundant or unnecessary.

I actually wouldn’t place orcs into this category because what they are is pretty clearly defined. I do think that The Battle for Wesnoth partially treats them like an all-creature, but they aren’t one as a whole.

That said, orcs do basically replace any “savage tribal peoples” that exist, so you could look at it from that point of view.
But orcs also don’t experience speciation in the same way that most all-creatures do.

Vampires are another one of the obvious all-creatures, evidenced mostly by Vampire: the Masquerade and Vampire: the Requiem.
However, this all-creature status goes back to Dracula. Dracula was also a werewolf, because he could control wolves and turn into one.
The Gangrel clan from Masquerade shows this vampire/werewolf overlap quite clearly, since they can explicitly turn into wolves. This also places Werewolves from Werewolf: the Apocalypse into an awkward position, since they aren’t the only werewolves in the setting.

I’d also argue that vampires who are a distinct race – that is, they aren’t a supernatural disease but reproduce like normal – are elves, which means that you could theoretically have every creature that overlaps with werewolves, vampires and elves all be…elves. Terrifying, I know.

I think werewolves are an example of a theoretical all-creature – in that you could have every wolf-like creature in folklore/mythology turn into a werewolf, and then undergo speciation – but, for some reason…this just doesn’t happen? I think this is because the modern conception is very rigid in what it is: a guy who can turn into a big humanoid wolf.
You know it’s bad when werewolves are absorbed into vampires.

That said, a more generic shape-shifter could probably absorb werewolves and Kitsune at once.

I used the zombie as an illustrative example, so I may not have to repeat myself.

Zombies are so ubiquitous that you can’t get away with creating any creature that is vaguely similar without someone calling them zombies. And there are so many types of zombies that I’m pretty sure most fiction that is focused around zombies features some speciation occurring. Even Minecraft has different kinds of zombies.