This makes everything ten times easier on you as the author.
|Trust me, building your own city is hard enough. You don't want to build your own world.|
Tip #1: Ask How Everything Has Been Kept Secret
There are two kinds of modern fantasy; the secret world, and the open world. The secret world is just that; a modern world where fantasy creatures and magic exist, but which are for one reason or another something the world at large does not know about. Jim C. Hines's Magic ex Libris series is a prime example of this (seriously, go check these books out), as is the World of Darkness series of roleplaying games. This style of world makes your life a little easier, because regular society ticks on with almost no one the wiser. It also provides the this could be real thrill that we all have when we look down a dark alley at night, and we wonder if that was someone taking a shortcut, or a vampire on the prowl.
That said, you still have to give us an explanation of why no one seems to know what's going on.
|You expect me to believe that was some swamp gas and a weather balloon?|
There are dozens, if not hundreds, of ways to do this. Men in Black show up to scenes of supernatural happenings and shush up what happened, the most powerful vampire in the city secretly controls the media and the police, there are so few creatures that incidents are few, far between, and happen in the middle of nowhere, or people just refuse to believe what they're seeing when it confronts them, for one reason or another. Whatever method of enforcement you choose for your world, you have to make sure it's both consistent and believable.
For example, if you have a vampire on the loose in the city and he's being hunted down by a special, supernatural division of law enforcement, that works. A single vampire can be written off as a crazed serial killer. But what happens if someone gets a video of this vampire putting his fist through an engine block, or security footage shows him disappearing into a cloud of smoke? In order for a secret world to remain secret you need to have believable ways to cover up what's happening, and in the modern world where millions of people have a camera riding around in their pocket, that can sometimes stretch belief if you don't put some thought into it.
Also, before you start thinking open worlds are easier, ask yourself how you'd give a life sentence to a vampire convicted of murder. Do vampires have rights at all, being dead? Can they get married, and can they purchase property? If someone is a werewolf, does that mean they can't get health insurance because of a pre-existing condition? Are religious organizations protesting those who have relationships with shape-shifters? How long has the general populace known, and what measures did governments and societies take? These questions are different, but no less complicated than keeping everything a big secret.
Tip #2: What Is Your System of Magic?
One of the constant features of most modern fantasy settings is the existence of magic. The question you need to answer before you even consider putting words on the page is how does magic work in your world?
|Don't laugh, it could happen.|
There are a lot of systems of magic. There's ritual magic, where you have to go through prescribed rituals including obscure items, saying the right words, and making the right offerings in order to have an effect. There's the idea that magic is about channeling your willpower (an idea espoused by Aleister Crowley and David Eddings both). There's the system where magic requires certain items (wands, rings, amulets, etc.) to access and perform. There's what I refer to as the X-Men method, which is that certain powers are handed down through different bloodlines. There's a variation of this I call the Not-Quite-Human method, where there was an introduction of something inhuman along your family line. Your great-grandmother may have had congress with a demon, you might be descended from ancient fae folk, or perhaps one of the old gods decided to appear to your mother in a shower of golden light.
These are just a few examples, but whatever method for your magic you pick it has to be consistent, and you have to define its limits. For example, can magic bring people back from the dead? If so, are there any consequences? Can it be used to travel in time? Make someone immortal? Give animals the ability to speak English? None of these things are out of the question unless you say so. If you're going to make rules, though, don't break them for effect. Rules are the realities of the world you're creating, and if you start ignoring them your audience is going to stop trusting you any time you say something is or isn't absolute.
Tip #3: What Creatures Exist In Your World?
One of the biggest, most important decisions you're going to make is which creatures do and don't exist in your modern fantasy story. For example, say your main character is a werewolf. All right, you have introduced an element into your world. What kind of werewolf is this character? Is it the "I change during the full moon, whether I want to or not" kind of werewolf, or is it the much sexier, "I change whenever I want to, because I'm in control of my own body," kind of werewolf? Is the change a curse like in some kinds of folklore, or is it a change brought on by wearing a wolf skin like in old myths? Are there other shape changers in your world, like the leopard men of the South American jungle, or the pink dolphins found along the Amazon who are rumored to change into men in white suits?
|Are were-goats a thing?|
Okay, so you've doped out your main character, his powers, and you've answered all these questions about shapeshifters throughout your world. Now you have to answer the question of whether or not there are any other kinds of creatures. For example, are there vampires? Werewolves V. Vampires has been a big deal ever since White Wolf did it in the World of Darkness, and it's been kept alive (undead?) by movies like the Underworld franchise. Okay, so you want to add vampires because the walking, human-eating dead are pretty common as far as world myths go too. Now you have to answer not only which vampire folklore you're going to consider true (does sunlight kill them, weaken them, or make them sparkle? Do crosses or garlic cloves do anything? Stakes, beheading, or burning?), but you also have to answer how that vampire folklore intersects with your werewolf folklore. Do werewolves who die rise as vampires, as some legends suggested? Can you be a werewolf and a vampire?
Every time you decide to add in additional folklore you have to answer all these questions, and make the chain even longer. If you decide to add in the Fair Folk of Irish mythology, or ghosts, or voodoo zombies, then you need to know how those things interact with the rest of the world. Are they all part of a common source (i.g. all monsters spring from the same womb, such as in Clive Barker's film Nightbreed), or does each kind of creature come from its own part of the world, with its own separate backstory?
There's another thing you have to consider when it comes to your creatures, though; do they have a boss? For example, if you have angels, that implies that somewhere just off-camera is the god Abraham and Mohammed prayed to. If you include rakshasa, that implies the Hindu pantheon exists (or at least existed), and if you have demons then it implies that, somewhere, the devil is doing his work.
Tip #4: Be Careful With Your Gods
Years ago, modern fantasy stories started bringing in gods as characters. Sometimes they'd just be there for the name recognition (we see this a lot in the Iron Druid series), and sometimes they'd be directly connected to the story (like we get in Neil Gaiman's American Gods). In this case gods are like your magical creatures, but writ large. Which is why you really, really need to ask yourself why they're here, and who you're letting in.
|And why, if Thor is here, isn't HE solving your problems?|
Some stories absolutely require the existence of some kind of divine being in order to hold the story's structure together. The Percy Jackson series, for example, needs the Olympian gods to explain their world, and why their leads have their power sets. It also justifies a lot of their monsters. In American Gods the whole point of the novel is the clash and competition of all the gods, both new and old, in America. Without their existence there simply is no story. Period.
That's all well and good. Gods are a lot like a double-barrel shotgun that occasionally goes off on its own; you really want to leave it at home unless you are absolutely convinced you're going to need it.
Why? Well, for one thing, because the existence of gods asks a lot of questions. Say you choose to put archangels in your story, and they fully admit that the Abrahamic god exists. Well, if we're to believe the source material, he's all-powerful. So if Yaweh exists, but then Odin and Zeus walk in on stage left, there's a BIG unanswered question looming over your story. Where does the power of one begin, and the power of the other end? Why, with such powerful characters clearly in existence and paying attention to the events of the world, is your protagonist even necessary? Why, if they clearly exist, don't these gods have more worshipers?
All of these questions have answers, and they'll differ with each author. But choosing to include every mythology and every pantheon is a lot like throwing every color of paint onto your canvas; it might look brilliant in your head, but if you're not both experienced and careful it will turn into one big, ugly mess.
Remember, It's Your Book
With all of this said, it's important to remember that this is your book. If you want to have shape-changing tigers who escaped from a zoo fighting a 10,000 year old vampire queen and her army of Voodoo zombie servants for the fate of a small town in Idaho, that is your right as the author. However, it is also your right to question aspects of the genre, and ask why doing things a certain way has become a genre trope. For example, why does modern technology always seem to go on the fritz when there's magic about (a trope I wrote about here called The Sliding Scale of Technology and Magic)? Why is there only a certain amount of spells you can use in a given day, which appears to be a holdover from roleplaying games like Dungeons and Dragons? Why do demons have to have bodies, even though their legends say they're formless spirits?
You can do things however you choose to, but you should always look at your decisions and be able to answer that all-important why.
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