Modern Greek has nasal Sandhi. That means that following a word ending in /n/, any voiceless stop is voiced. (And in the case of /ks/ and /ps/, so is the following /s/.) The /n/ in turn assimilates in place of articulation to what follows.
So:
As any search for “Quora” on Upwork will show, plenty of people are being paid to write answers on Quora, without being state agents. Quora has strictures against spam; it does not have strictures that I know of against propaganda.
From my outside perspective, I keep thinking Quora is one bad news story away from being in a world of hurt. But the bad news story hasn’t happened since 2014. And at least this year they’ve hired a lawyer.
Spam is not the right category for suspected professional propaganda or astroturf, but it’s close enough to serve for reporting, and it’s better than mere “factually inaccurate”. Do give an argument for your suspicion if you make a report, though.
Being a foreign word ending in a non-Greek ending, there is no plural. In Modern Greek, if a noun ends in something other than a vowel or sigma, it can’t be declined. (Nu is archaic; rho xi psi even more so.) So το βαμπίρ, τα βαμπίρ.
I see that at least one person online has named themselves Vampirissa “vampiress”, forming a feminine of the form. But that would be considered informal usage: formal usage would just put a feminine article in front of βαμπίρ.
There is a reason unassimilated loanwords suck.