First of all, writers go way out of bounds of the pure mythos.
They give vampires more powers than they really would have. They let them cross water, which they cannot. They let them enter houses without being invited. They let them survive in sunlight if they are old or if they stay in shadows. They let them feel for the people in their lives. They let them survive for hundreds of years without people wondering just when the hell they're going to die. They let them walk among the living without being noticed. They let them breath and bleed and have sex. They come up with more than the accepted way of killing them...again. More than just the stake through the heart...now you gotta cut off their heads. Not a bad idea, if you should find a willing vampire. The cross, or mention of the Supreme Being, will also put them off, as will garlic. Yeah, right.

Wrong!

Werewolves...well, they only turn when the moon is full. That is exactly one night a month. One night. The myth doesn't say "when the moon is nearly full", it says "when the moon is full". One night. That's it. And they can be killed by silver bullets through the heart. That's it. Silver can hurt them, but not kill them unless it is through the heart. One measly night to worry about. That isn't bad enough. So they change the mythos and wham! You get werewolves turning when they get pissed off, like The Hulk, not Lon Chaney. Phooey. Stick to the trick. And recently, writers have decided to allow the wolves to turn while having sexual relations with humans, or be able to turn it on and off at will. A vampire is always a vampire, a werewolf is only a beast one night a month. AAARGH.

Let's move on to ghosts. Ghosts cannot harm a human being outside of frightening them to death if their hearts are particularly weak. They cannot stab them or shoot them or bite them or scratch them. They might scare someone into losing their footing, however, thus enabling the frightee to fall down stairs or off parapets. They cannot really enter into other person's bodies, like living beings, and direct them to do this or that. Nope. We'll have to leave that to demons...which can and do take over humans and bite and scratch and kill. Demons, well, that's a little too theological for me. I am still wondering whether they exist or not.
And if they are minions of the Devil, well, I doubt it exists, also, but again, God has no place in this diatribe of mine.

God is. Nobody writes about the mythos of God with any authority. Well, there are people who constantly assume or presume they know what God does, but well, I wonder whether God knows there are people who claim to know what's going on in God's head.
If I were God and people acted on my behalf like they claim to, I'd probably scorch them for being presumptuous. Of all the stuff people think God does or ignores or wants or would do...well...mortal beings are pretty uppity to think they can outguess God.

So, we move right along to gods...those creatures worshipped long ago, or currently, with stories of their own that go back in time. Legends. All sorts of stories supposed to teach mortals how to live the right, or godly way.
Several religions have trickster gods. What if a person decided to emulate the trickster? The world would be a mess.
Hey, wait, the world IS a mess. Hmm.

Moving right along with the supernatural creatures, there are fairies, or the fey. They're supposed to be tiny creatures that live in forests and flowers and toadstools. They are, in Tolkein's version, large and powerfully magical. Dunno. They separate themselves from humanity. They can flit about from flower to flower. They have wings.
They apparently can get larger at will. They cannot cross iron as it weakens them. They usually are not harmful to humans, more of an annoyance, really.

Trolls live under bridges and are basically stupid. They carry clubs and hit humans and are very dangerous in their stupidity. They're ugly and thus dangerous. So, avoid trolls.
Since they aren't bright, they can be cast as bad guys in a story, but they apparently would be easily outwitted by any normal human, so that doesn't make for much of a story, now, does it?

Witches...well...they're either beautiful or ugly, male or female. They ride broomsticks across full moons. They have cat familiars, their pets, or sometimes the familiars do work for them, carry messages, talk them to sleep, carry diseases off to plague the countryside and innocent folk. Witches can be killed by drowning or poisoning or stoning or having heavy weights dumped on them...just as can any mortal human. Witches are probably the most written about, the least effective and the most modernized because of this idea of Wicca, which is in no way related to witchcraft, but instead to the Old Religion, whatever that is. It probably has an earth mother goddess, but this new stuff is just someone's idea of a religion based on nature. It is in no way related to the idea of witchcraft which was never, ever written down. Anywhere. It is all in the minds of individuals looking for a way to barbecue old ladies or pretty girls who get in their way.

Then there are the mythological beasts, griffins, krakens, mermaids, selkies, (mandrakes), dodos (they did exist) and dragons. There are others in various cultures...chupacabras, mothmen, were-anything, bigfeet, various lake monsters...all of which are along the same vein as the earlier ones depicted at the bottom of old maps and in bestiaries dating back to the time when people still believed ugly old women could curse you.

Why do these beasts, these demons, these witches and angels and giant serpents and killer creatures exist? Because bad things happen without explanation, that cannot be explained by logic or science, so fantasy takes over. That boogeyman in the closet, that monster under the bed, the creatures of our nightmares exist in our minds no matter how advanced we get. As long as we have dreams, we have night fears. Racial memory of what can happen to us in the dark clings to us still and probably always will. Knowing that there are no real monsters that are not human does not make the terror of the night any less real in our minds. It is the dark, and what we cannot see in the dark that makes all these fantastical creatures that want to harm us come to life.

The thing about monsters is that fiction writers always come up with a way to kill them.
Just catch that vampire with a stake and drive it through his or her heart and it ceases to exist. Slugs of silver will kill the werewolf if your aim is good enough. As Harry Potter found out, a sword through the brain will kill various other beasties because there has to be a way of killing them. Fry witches, drown 'em, crush them...they'll die and we'll be safe. A belief in God should be enough to ward off these beasts, but somehow, it never seems quite sufficient.
We need a way to act to save ourselves.

More than prayer.
More than shutting the closet door.
More than not inviting in strangers to our houses who might prove to be out for our blood.

H.G. Wells had Martians invade the earth, wreaking havoc all over the globe. They seemed unstoppable...our worst fears come to life from outer space. What kills them after they do a good job of wrecking most of the civilized planet? Bombs? Fire? Water? Ice? Chemicals?
No.
Germs.
Earth germs.

Microscopic things we all endure naturally, but the Martians weren't used to our germs.
HG did a good job of chasing away those boogeymen.

What must we do to get our stories straight? To become enabled to destroy that which we fear most? The monsters of the ID?

We have to stop breeding maniacs. (Especially ones that rule countries.)