Magic

So, there are a lot of magic users in Valoran, right? Hell, practically everyone uses some form of magic. Here's what I think-

Firstly, you've got your magic-users divided into three categories:

-People who are containers for magical power, no matter how great or how small. Their effects when using magic are large and oftentimes explosive, and require both immense amounts of control and concentration. People like this include Syndra and Ahri.

A lot of times, it's rare for someone to be born with huge magical potential (in this case, potential meaning "containing lots of magic")

However, this does not mean that it is rare for people to be born as these "containers". Many summoners and champions are containers, who are hybrids with one of the next two options.

-People who draw, or summoner magic from a natural resource. The amount of magic the resource has plays a factor in the effect the person makes, but the individual's control is far more important. People like this include Sona, Irelia, and Karma.

"Natural resource" is a very vague term, and will be covered later on in this post. 

Summoners are mainly composed of this type of magic-user. They draw the raw power from the nexus crystal to summon. 

Even the most large and infinite magic an item contains is useless in the hands of somebody incompetent.

-People who are completely, one hundred percent magic. Their body is literally the fifth form of matter, superheated to go far over the temperature of plasma. They are no longer containers, but complete sources of magic. Magic users like this consist of Xerath. 

Xerath is the only champion who fits this category.

Fiddlesticks and Hecarim are maybes for this category, but most likely placed in the "container" section. 

Natural Resources

These resources range anywhere from a small piece of rock to an entire island. Ionia is a key example of these natural resources. It is a place buzzing and humming with magical potential, as well as (but not limited to) Shurima, parts of the Freljord, and the Shadow Isles. Many Ionians can tap the natural energy of Ionia, and therefore many citizens of the island are mages. Irelia and Karma are key examples of this- their will and power are, as I believe, strongly linked to Ionia. Valoran itself can be considered a Natural Resource. Champions like Ahri and Lux can concentrate a large amount of this energy into one space, and then bend it to attack or heal. 

This doesn't mean that Natural Resources are limited to physical items. These can be entire universes, or different planes of existences. For example, Lulu draws magical energy from the Glade, a completely different world from ours. Malzahar takes the magic from the Void, and Soraka uses the magic from the Celestial Plane. Oftentimes, people use gateways to take magic from one space to another. Lulu can use Pix to act as a gateway between her power and the Glade's. Others can take power simply from command, or will. It is important for somebody to have a strong link to the alternate universe, or they may be consumed.

Then, there are magically tampered items. These include Ezreal's... thing (crossbow?), or Ashe's bow. These items can be infused with magic, born to magic (very rare), or simply be powered by a rock placed inside/on said item. More examples: Riven's sword, Irelia's blades, Varus's crossbow, the item in the box for Zed, etc etc.

One is not limited to taking magic from a single object. Karma, for instance, can tap both the magic of Ionia and that of the Spiritual Plane. Irelia also uses Ionia's reserves, as well as her blades (though it is up to debate whether it is her controlling her blades, or her blades controlling her).   

And that's the basics. Tell me if you disagree, agree, etc? :D Special thanks to: