This can include inserting their protagonist into real historical situations, in an attempt to convey the age of the supernatural in question. Unfortunately, this usually leads to some sort of revisionism as an imaginary character, would have had no role to play for the allies in WWII. Yes, I am looking at you Sanctuary. Kevin Hearne, had his protagonist Atticus play a role in the French resistance. In Eternal Law, Zak became the Angel of Mons (which is based on a real legend), who guided soldiers to safety in WWI, and was then punished for his action by being forced to defend soldiers accused of going AWOL. Rebbecca Hamilton inserted one of her characters into the Salem witch trials, and in Morgan Rice’s Vampire Journals series, she took it a step further and even used one of the historical people from the trials.
The worst of this marginalisation is, of course, appropriating marginalised identities and equality movements. If there were an award for squeezing in the most appropriation in a series, it would have to go to Dan Waters who wrote The Generation Dead Series. Waters has managed to appropriate slurs, appropriate the language of disability, refer to the closet, passing and coming out to describe his zombies revealing their true nature, as well as appropriating the language of the civil rights movement, and appropriating Jim Crow, to apply to the separation of the differently biotic (yes, he actually used that term) and living people.
Carrie Vaugn’s Kitty Norville series has referenced vampires and werewolves coming out of the closet in nearly every book, and has referred to discriminating against werewolves as akin to the temporarily able bodied discriminating against someone with a disease. Laurell K Hamilton’s Anita Blake series does this repeatedly - lycanthropy is a disease and anyone discriminating against werewolves is presented as ableist, even though the word isn’t used. It is even overtly said that discriminating against a werewolf, is like discriminating against someone with AIDS. In True Blood, we have vampires who come out of the coffin, and are opposed by right wing religious people, who counter with God hates fangs. Sookie has on more than occasion equated hating vampires with racism. For his part, Bill Compton, Sookie’s ex boyfriend, decided that it was okay to invoke the civil rights movement. Kim Harrison is fond of acquainting racism with the treatment of pixies, who are fictional creatures. Harrison has gone as far as to assert that the word bug is a slur, when used as a descriptor for pixies.
Even when it is not overt, the undertones make the juxtaposition readily obvious to any thinking person. In Nicole Peeler’s Jane True series, there is much discussion about the fact that haflings (read: people with one supernatural parent and one human parent) have difficulty fitting in with both human society and supernatural society. Peeler’s writing very closely mirrors the experiences of bi-racial people, though she stays away from making a direct comparison.
Of course, very glaring is that vampires, werewolves et al aren’t oppressed and weak even in their fictional worlds. Quite the opposite, they are hyper-able, capable of things beyond even the strongest and most powerful human being - constantly it is presented that the only way humanity can bring down these creatures is through overwhelming numbers. The idea that superhuman beings are being persecuted by humanity is such an incredibly different dynamic from marginalised people’s experiences that the implied comparison is gross. And, of course, humanity often has a reason to be wary of these creatures. It’s prejudice to fear the vampire - when it actively hunts humanity? It’s prejudice to fear a werewolf that rampages with claws, fangs, superhuman strength and ferocity? This doesn’t feel like prejudice, it feels like common sense.
We see this overtly in the TV series and books themselves. While True Blood is always happy to play the oppression angle, there’s not a vampire on that show who hasn’t left at least one human corpse in their wake - sometimes several. Yasmine Galenorn’s Sisters of the Moon Series, has predatory vampires and a full range of lethal, dangerous fae, who don’t place any real value on human life. Many characters in Laurell K Hamilton’s Anita Blake series, may lament anti-vampire and lycanthrope prejudice, but we see over and over that even these creatures themselves think they need autocratic, draconian bosses to keep themselves in line.
Another gross element of appropriation, is appropriating human disaster and atrocity and putting a supernatural element in them - or worse - attributing a supernatural motive for them. The strongest example of this I can think of is Grimm, which recently presented Hitler, as a supernatural creature. Lost Girl has had its share of fuckery by attributing the genocide in Darfur to supernatural causes.
Why is this gross? This approach takes a monumentally awful moment in human history, and uses it casually for entertainment and story advancement. And it is notable in these examples that it is rather casually inserted. Grimm could have fully portrayed the power of the coins, without invoking the Nazis - let alone Hitler himself. And the spider monster in Lost Girl, was already obvious in how dangerous it could be, without invoking the actuality of human genocide.
Furthermore, it rewrites history in a way that spares human blame, or shifts the focus away from the evils committed by humanity. It becomes either about the supernatural, or because of the supernatural. These are not things where the focus can be allowed to shift - the sheer enormity of these events cannot be diluted or diverted. But worse is shifting the blame to woo-woo. The evil atrocities of the Nazis or the horrendous tragedies in Darfur, were because of human hatred and human evil. We do not need a magical creature or a demon, behind the evil, nor we do not need the influence of woo-woo to explain why they did what they did. It was humanity, the blood was on human hands, and it’s intensely disrespectful to shift even a drop of that blood, an iota of that blame or a speck of the responsibility for these terrible actions. These evil people did not need magic for their evil - let the blame lie where it belongs and don’t appropriate their victims for our stories.
Appropriation of the histories, and experiences of historically marginalized people has been quite normalized, as you can see from this post. This is frustrating because in many cases, we still have not achieved good and equal representations. This suggests that our lives are only valuable when they can be appropriated to serve the needs of the plot or a privileged protagonist. It serves to further "other" us and reduces or experiences and our lives.