People talk of monsters as though they're only fairy tales. I'll tell you the truth, there's things out there, but they aren't anything like what you've been told about. Yes, you've been told that pretty often too. Ha ha. But I'll tell you, there's two types of things out there beyond where mankind has seen in centuries: animals and monsters. And monsters, real monsters? They aren't anything like what you've been told they are.
See, people confuse animals for monsters often. It doesn't matter if you've never seen anything like it before. It doesn't matter if it's a big rabbit, or a small tiger, or even if something walks on two legs and carries around spears. There's an argument for that last one being people, but not monsters. They're entirely flesh and blood, the same as you or I. They live their lives, have the same motivations as any other animals or people, and they're just as scared of real monsters as we are.
Real monsters, they aren't entirely like us in that sense. Most of them have at least some flesh and blood, either as parasites or as a mix or just as some kind of costume. But there's another layer to it. Call it "magic," call it whatever. I'm sure in this day and age people can come up with a better name for it. The point is that it doesn't follow any laws of physics as we understand it. Hell, maybe the stuff creates it's own laws of physics, I dunno. It comes in a few different forms, but it's not something that humans or other animals innately have. So put that out of your head, people aren't born wizards.
One of the weakest kinds of monsters is a parasite that latches on to people. You can't see it or feel it, it doesn't even really exist in any physical way, but it messes with a person, alters them. Strong starlight forces it to hibernate, something about the radiation maybe, but when it gets enough breathing room. . .it comes out. Takes a person's body and warps it out of control. Ones that don't have any kind of set "blueprint" are the nastiest, they just keep tugging and tugging until the victim is just a mangled pile of flesh. But once they've claimed one victim, they have an identity of sorts. And as for the next thing it jumps to. . .it tries to pull it into being whatever the first thing was before it tore it to shreds. You may not believe me, but that's what Lycanthropy is. It's a lot more than wolves, but wolves were the only ones to survive for long on earth after the isolation period started. The transfer by bite? That's how it reproduces. It buds off a piece of it's existing "blueprint" and shoves it into another host. Each time one manages to successfully make a brand new blueprint from the initial botched attempt and then transfer to a beta host, that's a new strain of Lycanthrope. Usually they'll hit some animal in it's sleep and then a human or other curious intelligent species will notice the deformed corpse and come into transfer range for that to start.
But that's just one of the weaker kinds of monsters. They're not super common, not super scary, heck you don't even really need silver to take one down. You want something really horrific. . .they get bigger. A lot bigger. The biggest monsters we know of don't need a host at all like the little ones, they can just eat some dirt and rocks off the ground and make any kind of body they want out of it. It doesn't even have to be a body made of rocks, they can take rocks and turn it into gold, or flesh, or trees that grow plastic outhouses for all they care. The only reason why they're the biggest that we know of is because any bigger monsters out there probably can't even comfortably fit on a planet. These things. I can say that they're so and so meters tall, it doesn't mean anything. I can say they're as big as so and so object, it barely offers a point of reference. But if one were to stand up like a person in a sort of humanoid shape with every last bit of it's presence and look you right in the eye, it would cast a shadow as far as you could see. You under that shadow? Oh, good, it's probably blotting out the sun, too. Not that they won't emit their own light or something. And they can shatter into pieces, too, each one still fully under it's control as thought it were still part of the main body. You want to know how people get magic? If you're stupid or unlucky enough, one of these things might worm part of itself under your skin. Make itself cozy. Start invading your thoughts, messing with you a lot like the little ones, but instead of one fixed possibility there's an infinite number. People make pacts with these things, worship them like gods. I wouldn't go that far, but there's a reason why that is. And you darn well better not risk finding out why.