On the matter of Magic Users

Magic capabilities are determined by two factors: Genealogy, and the Erelith itself.

Some races more commonly bear the genes to cast spells/amplify their magic, though there is a large portion of Erelith that cannot use magic. Some individuals -- born with a rare combination of genes that leave them with unfathomable heights of power -- are invited to join the Artifice, a group of inventors in Kalold who research and develop technology influenced and fueled by magic. These individuals are capable of impossible feats; from shifting the mountains to restoring souls to their vessels (bringing the dead to life).

These genes were not without their burden; the more sensitive a being was to the magic and capable of using it, the more frail they were. This often rose up by means of afflictions and physical disabilities. A man could be capable of bringing down a castle with an earthquake, yet die from a bee sting.

Experiments are conducted on captured mages to see what enables them to use magic (an irregular organ, etc).

The other factor is the 'levels of magic' in Erelith. The magic itself is drawn into individuals through the atmosphere, who can use the raw energy to conjure, destroy, alter and so on. The higher the magic levels, the higher the limits are on output, and the easier it is for a magic-user to cast a spell.

There was a period of time in Erelith where the magic levels were so low, even the most gifted of individuals could do little more than a fireball. With their research threatened, Kalold devised a way to replenish the magic in Erelith; the Infinity Spire. It was the pinnacle of their most brilliant minds. It could draw in magic from other realms, and revitalize the concentrations in Erelith.

Due to some mishap -- some speculate it was punishment by the gods for twisting the hand of destiny, others sabotage in fear of the Infinity Spire’s power -- it exploded. The rubble that cascaded from the heavens contaminated Lerem -- the land it was built upon.

Auras
The term given to the background 'magic energies' throughout Erelith. Auras are channeled through the caster during an Invocation, to be manipulated into what the caster desires. Some areas are oversaturated in the Auras, while others are starved. This impacts the potential magnitude of spells, as well as how much of an impact the Auras have on those sensitive to their presence.

Aura Types
While the Auras can be reformed and used as the Invocation sees fit, some Auras are aligned with certain manipulations. Life Auras are abundant in Oner. Death Auras are palpable in Omem. Utilizing the type of an Aura allows for more powerful Invocations with a smaller strain, whereas utilizing an Aura's counterpart (Death Aura for Life Invocations) will have the opposite affect.

Affinities
Much like Aura Types, mages have an innate Affinity with certain types of manipulations. Some are natural-born healers, whereas others struggle to mend a small cut. The greater of an Affinity one has to a certain manipulation, the greater of a disadvantage they will be at with its counterpart.