I don't think your greninja or argonian characters are in trouble. The large companies who owns pokémon and elder scrolls aren't likely to lash out at an individual who uses the species they created in the way you use them. They don't lose profit over it.

It is more likely if the character/species belongs to another individual or a small independant company though.

Though Nintendo might. But if that happens, you're fucked. But since Nintendo is unlikely to look on fa, you should be fine.

Yes it can, but if you know how copyright works, you can write around it easily.
The thing is, to be copyrighted the work has to be distinctive in it's own right.
Quite a few of the 'closed species' in the Furry Fandom don't make the cut. They are simply too stereotypical. Just as an example, a Fox species with a different fur colour won't make the cut in court, especially if there is no background like history, culture and so on.

If you want to be on the safe side, just don't mention what inspired something in the first place. Even, or especially if it's obvious.
Not that many would know the differences between an Argonian or a D&D Lizardfolk, which may be just a cultural and style difference in architecture and fashion.

Edit: And Nol made a good point.

Some actual unique species don't even make the cut. Protogens for example while claimed to be "closed" at a certain level are actually not copywriten anywhere. The one place their creator did attempt to get a copywrite (Australia) actually denied him. Why I'm not sure, but still. Point is you're fine Kiala, all this witch hunter can do is send a bunch of nagging children at you xD

While unique, the Protogens are not 'distinctive' enough. Not from a visual point of view because every individual can look very differently and (as far as I know) there is not enough background. And it can get even more messy.
There is a Science Fiction Pulp series that has been going on for 60 years. They have a machine species called the 'Posbi'. Predating Star Trek and the Bog, their cube-shaped ship design has essentially been 'stolen' for the Borg Cubes. The name 'Posbi' may be protected, but as long as you call them differently and avoid specific terms you can use them rather freely. And the Borg? Considering that's the short version for Cyborg?

The same goes for the many Superman clones or stories that 'stole' the Superman background of a last survivor of a species getting superpowers on earth. DC Comics has given up suing those a long time ago.

Copyright is a messy thing. On one side, if you know what you are doing it can be easy to get. At the same time it is easy to write around it.

What 'stuff' has been going on?

All I'm gonna say is, Blizzard, fucking Blizzard tried to put the boot on Overwatch Smut art. The fact that the porn community for it is still active, but the... actual playerbase isn't, that should tell you how well that went. And if a major company with all the legal resources anyone could ask for couldn't enforce any kinda genuine ban, nobody can.

I wouldn't go worrying about it.

Drama, drama is going on. Another entitled individual thinking someone stealing theit OC because it looks slightly similar and claiming it's the same species as the one they came up with (totally on their own, without any input from outside), which is their species and theirs alone and noone else is allowed to draw pictures of that species without their explicit consent. Because it *GLOWS*

Lol, I know what this is about

Eh, don't worry about it, the guy who started the drama deleted his journal anyway.

Oh wait, I'm sorry, I've been informed that I need to set the record straight that his journal was deleted because it violated TOS. Not sure that's better, but I have to set the record straight.

Considering he started the witch hunt for dumb reason against someone else... he's lucky he
Is account is not suspended

you should be fine. I don't think the companies would be that petty.

Depend, if it's for commercialized or no. If you don't produce
money with your oc and that it's a bit inspirated from another Original specie (like Argonian or Greninja), I don't thing you will got problems. Your oc has free copyright (In France, you got automatically a copyright. For USA, you need to give deposition for intellectual property).

In the case you commercialize it, there are issues. Look at Bunga from Lion guard serie (Lion King. I seen it on the french wikia (not sure) this last oc was inspired from Spike (My Little Pony). Even if it's was true, if you have enough originality and you got more than one inspiration, with maybe changing a bit the chara design like psychology or archetype, this can run normally.

Bunga has a very different design and psychology from Spike despite getting inspiration.

Hope I said is good.

This sounds like bullshit. You're more than likely to be fine.