In a high magic setting, how should I introduce "unnatural" magic?

Question

I am going to run a game of 13th Age, which is pretty high magic - the industry of the world is primarily enhanced by ritual magic (wind elemental bind to sailing ships, rituals ensuring good weather for farming).

I would like to introduce a form of unnatural magic to the game (mostly for the enemies), something akin to magic found in the Call of Cthulhu games. How do I make it unwholesome, unnatural and more importantly, scary?

Just one clarification here - I still want the default high magic setting, but I want the PCs to come up against cultists who use this form of unnatural magic as their particular foe.

Answer 1

In order for magic to seem unnatural, it needs to have noticeable difference from the "natural" magic that it's being compared to.

Along with the other answers, consider allowing the unnatural magic to break some of the rules of natural magic (or all magic as the PC's previously knew). In order for this to work you need at least a couple well defined limitations to normal magic that the party considers "just how magic works" so that breaking the rules has more impact. If you have to you can make this something only some of the party can pick up on that's purely fluff, but if you can bake it into the mechanics themselves all the better.

Alternatively (though this is more difficult to sell) you can have the unnatural magic suffer from limitations and jumping through hoops natural magic does not, but gets something else in exchange that makes it worth it. It could even noticeably not actually be magic as the PC's know it; despite looking, sounding, and burning like real magic.

Something like this has the added bonus of being something the characters can discover without being told. If the players notice the contradiction from the norm and investigate further of their own accord, it will be much more of a mystery than if they're told it's unnatural. Of course if some amount of mystery about the unnatural magic isn't your goal this could actually be counterproductive as it may make the PC's think of it as one and go off chasing it...

Answer 2

(I haven't played 13th Age, but this sounds pretty system agnostic.)

Start the campaign with no usage of the unnatural magic, and have it be introduced with, for example, the first "mini-boss." Increase use of it after that point. To further the difference, give the "unnatural" magic a different name, like witchcraft, demon-magic, old-magic, depending on the feel you want.

In order for it to feel "unnatural", the "natural" magic has to be established first. Introduce them well to the common-place setting of the ritualistic magic of weather, fire for forges, etc. Note to the players that the magic is part of everyday life.

Introduce the unnatural magic in an environment that has all of the features you want the magic to have features of: dark, creepy, scary. A deep dungeon of demons or abandoned temple of old-magic worshipers are some ideas.

When the magic itself is described, ensure you mention what is happening when the magic is cast. For example:

"The cultist summons a ball of unnatural fire from the beyond! As it manifests, you hear the screams of a hundred souls before it hits the wall near you!"

Other examples could involve bad things happening to the caster of the magic, such as draining life force or grotesque side effects. Keep it creepy!

Answer 3

If magic is commonplace, you'll need to be able to emphasize the unnaturalness of the evil magic in a special way that sticks out and is unusual. Something like:

1. Strange power source. For example, make it be fueled by cultists injuring themselves or others and your players should be shocked. The shrieking man drives a knife into his hand and waves it at you madly. Waves of black fire burst forth and stream towards you

2. Casters think it's different. This might not be to your taste, but a gloating cultist who talks about how he's found a better, stronger magic than the PCs have will definitely get their attention. Whether it's actually stronger is up to you, but your PCs will want to know what this supposed wonder magic is.

3. Different name. If the weird magician gets offended at being called a magician and proclaims that he is actually "Zanzibar the Third, heir to the powers of the Unspawned Darkness who doesn't need any of your pitiful rituals/spells" it should make your players suspect that it's different.

Answer 4

I'm not quite sure if that's what you mean by "unnatural", but if you want to make magic inherently evil, I suggest to make it powered by sacrifice of the unwilling.

Make the cultists keep chambers full of slaves (human or other empathy-inducing creatures, such as fairies) who suffer and weaken (and eventually die) every time the magic is cast, through some "life force" or such being drained out of them.

Freeing those slaves could make for a nice side quest.

Answer 5

Unnatural magic must feel different than other forms of magic; when I need to do this it typically comes in one of three forms (or as a hybrid of the above):

Uncontrolled Magic

Typically, magic is a tool; it may be a contractual thing, but it is always done, at least in a normal fantasy setting, with a certain degree of control, conscious or not. When I have unnatural magic, I find that a key element is that it can't be controlled-high fantasy settings view magic as a tool or a science, while unnatural magic is either unexplained or uncontrollable.

Different Methodology

One game I ran had an odd magical system; it was a world where everyone had magic, but they accessed it in different ways according to their training/abilities. The creepy magic, however, involved invoking outside powers into the world in order to gain favor and power; in essence, a faith-based magic that wasn't always derived from particularly happy deities. Needless to say, it was pretty obvious when someone invoked on you rather than casting a normal spell.

Corruption

Shadowrun has a Background Count system as well as Toxic/Insect/Various Unhappy Things that interfere with normal magic, typically more on a spirit world level, but also just for any magician. Unnatural magic will feel weird to those who can detect it-I'm not familiar with the setting you're discussing, but typically scrying of magic is possible; especially when magic involves contracts with spirits and forces of nature. Unnatural magic uses spirits, forces, and raw magical energy that no longer functions like normal magic does.