In my world, there are spirits. Spirits are… they're not things you want to get involved with. They have their own agenda, and they don't care who gets hurt. Even helpful spirits are dangerous, because they don't understand the concept of death. They're more likely to kill the person they're trying to help sometimes.
And then there are daemons. Unholy mixtures of flesh and spirit, driven mad by a forced possession. They are twisted beasts that only have the slightest semblance of humanity, and use magic in their quest to wipe out every other race. Magic is the mark of a daemon, and it is hated, and feared, and shunned. There are others who can use magic without becoming daemons, but they are mostly extinct.
The magic comes from souls. In drawing upon souls, you can tap into the energy stored there, the same as spirits do. Daemons pull on their spirit-soul, as their human-soul is pulled apart by the strain. Fae-users tap into their own soul, or can receive help from ancestor spirits. The downsides result in soul-sickness, or, in extreme cases, your soul is erased, leaving your body an empty shell. Generally, the body becomes fatigued before any of these come to pass.
Ley-users use "artificial souls". They travel to Ley lines, and tap magic from the earth. They then tear apart their soul, giving part of it to an object, using the Ley lines as a grounder. It is traumatizing, and some people do not survive. The result, however, is an "artificial soul". Something with sentience and powerful abilities, which can be used by the creator. The price for using Ley magic is not as steep as the others, but it is still severe. The Ley users have a telepathic link with the object, and some Ley users have gone mad because of it. Overuse of Ley magic places strain on the artificial soul, but the user feels fatigue. If a Ley user doesn't trust their object, and if the object doesn't trust the user, the strain can lead to an early death.
The casting of magic (what, you thought I was done?) is unique to this world. Rather than incantations, or gestures, magic is cast through song. The last mages went extinct nearly a hundred years ago, but there are mentions of people who drove away evil with the purity of their song in the holy books (and this is why prayers are sung, and why singing is so important to these people).
Sorry for the long post, but my magic system is something I've put a lot of thought into!