“Being influenced by” is not the same thing as plagiarism, not even close.
Plagiarism is where you quite literally take someone else’s idea and try to pass it off as your own, possibly making very minor amendments.
Now within fantasy themes there are a lot of tropes that are borrowed by all creators…for example GW2 cannot claim plagiarism in this case because of use of the term “Sylvar” as that term has specific meanings and is used by all fantasy creators in some place or another, so unless blizzard have literally recreated the race but renamed it, it’s not plagiarism.
Where you see plagiarism it can easily be argued that blizzard are simply drawing from the generic pot of fantasy influences and mythology, same as the individuals you’re accusing them of copying from did. I mean take Nurgle. The idea of fleshy, crafted death-like beings being associated with plague is not something Games Worskhop can claim is copyrighted to them, because the idea goes back to literature like Frankenstein, Black Death literature and the general victorian-era preoccupation with death and emerging biological science.
So unless The Margrave is quite literally adopting the mannerisms, attitude, behaviours and a very similar appearence to Nurgle, claiming it’s plagiarism is a huuuuuge stretch. The character is what GW can claim copyright over, but not the themes it was crafted from, which is what blizzard are arguably using.
I mean, what next, Tolkien’s estate suing anyone who uses elves? I don’t think so. The lore predates even him. WHolst the particular elven characters he created are protected, you’re going to have a hard time demonstrating someone is plagiarising his work even if they’re writing elves with very similar behaviours and mannerisms because it’s considered part of “common canon” now.
Ironically it’s blizzard who need to watch who borrows from their work. Recreating oft-repeated fantasy tropes is not grounds for plagiarism. But blizzard often spin them a little (ie Trolls who use voodoo and are inspired by Haitian/african culture). This is very much a blizzard unique insert (even if the themes the trolls borrow from are not) so where another game starts to include trolls that also use voodoo for example, that seems to be plagiarism because this is not an idea that exists in the fantasy canon in the main so it would be difficult for someone to prove they just got “generic influences” when writing such in such a way that shows they didn’t quite literally mimic blizzard’s process in doing so. I mean, there is nowhere to go that associates trolls and voodoo except for the blizzard universe. So it’d be a case of someone claiming “yeah I came up with this all by myself, that had nothing to do with it”. Doubtful.
It’s different for tropes, because pretty much every fantasy mythos/canon etc uses the same themes so it’s not a stretch for someone to argue “oh yeah I just got it from x mythology” because that’s entirely plausible.
So to go back to trolls for exmaple, let’s say you write trolls as a big, greenish, strong and somewhat dull race.
Baldur’s Gate, NWN, Everquest, D&D all use the same trope, and they drew it from stuff like scandanavian myth and the myths of europe regarding trolls, point is you could look in 100 places and get the same information.
Now let’s say you create a game where trolls use voodoo magic and speak with african accents. There is only one place currently that makes such an association: the blizzard universe. You will have an extremely hard time proving you came to exactly the same creative idea, but it was entirely uninfluenced by blizzard’s idea and was make in complete ignorance of the fact they’d done so already. You’d need to prove how you came up with it originally, and from whence it came, and as said, no canon on it exists, so you’d essentially be arguing from a position of “yeah well I just came up with it on my own just like they did, it’s just coincidence it’s similar” and in that situation blizzard would easily be able to pressure whoever it is legally to get it changed and there would be a strong case for them to get their way on that.