So, let's get down and dirty on the whole magic thing.
Who has it?
Only non-human creatures, specifically spirits, faery, sprites, and other such mythical critters. Humans themselves have no innate magic, meaning they aren't born with it and can't "magically" gain magical abilities. There are no human wizards shooting fireballs in this world.
How powerful is it?
Depends. For the most part magic is relatively low key. There is lots of manipulation of the mind and the environment, but again, no fireballs or crazy magic (at least not intentionally). I don't want magic to be a force that can essentially destroy the world through a single creature's hand. No evil magic-weilding overlords and stuff.
Can non-magic folk use magic?
Yes, actually. Even though humans don't have magic, there are elements within the world that contain magic within them. Gnomes, for instance, cannot come to life unless they are built by human hands; the clay itself is magical. Then there are other substances that can be manipulated using alchemy/chemistry, which produce results that can, for the most part, be controlled. Healing potions exist in Altern.
Having said that, I do have one substance that I've created that will have unstable results:
Very similar to cactii. They're sort of a mixture between a vine-like plant and a cactus. Cacticles, however, contain properties that are completely unstable and, for the most part, uncontrollable. Every time you use cacticles for any purpose, the results are random. A person chewing on the plant might light on fire, or turn to stone, or float away, or explode, or a number of other things. As a result, when experimenting with the plant, a lot of precautions are taken. For instance:
A person chewing the plant will stand in a bucket, be chained with thick metal that can't be burned or melted (and so the person can't float away), then be surrounded by thick walls, in case of explosion, etc. Every time a new result is found that is potentially hazardous, a new element is added into the mix to prevent damage to innocent bystanders.
So, the point is that cacticles are extremely potent, making them exceedingly valuable for study, since the potential of the plant itself is limitless. The problem is that controlling it is just about impossible (or so the human folk think).
Why do I want it like this?
Well, to be honest, I'm about sick and tired of all the fireballs and super magicians. I'm more interested in making the human more of an outsider, sort of how we might be outsiders in this world if magic were ever to be proven to exist (or mythical creatures for that matter). Or perhaps the magic folk would be the outsiders in this world? Well, in my world, the outsiders are the humans, since they are the ones mostly out of touch with the natural elements surging around them. As a result, they become isolated or targeted by the magic community. I wanted magic to be limited on purpose, because I don't want there being the possibility of super overlords and what not.
Humans will, of course, have ways of using magic, just not directly. They're means of magic is limited too, since it revolves around understanding natural elements and plants and being able to manipulate them to do what one wants. One can't just go "abracadabra" and make a magic healing plant. It takes time and dedication to find the right formula. Cacticles may have immense power, but that power is uncontrollable. One would have to have tremendous luck to use it for evil means and not explode or die in some other horrible manner.
I think that's more than enough on magic for the time being!