Human beings in the Endless Isles are not inherently magical. Rather, through study, sacrifice, or just dumb luck they can find a number of ways to tap into the power of the gods, spirits, and monsters that inhabit the world around them. Magic users are feared throughout the Isles, and rightly so, for even the wisest among them has in truth only the most rudimentary understanding of the forces that they wield. The people of the Endless Isles therefore look at magic users in much the same way your or I would look at a monkey holding a rocket launcher.
Mechanically, the use of magic in Endless Horizons is probably the largest difference from normal D+D. Spellcasters have extremely short spell lists, reflecting the fact that their spells are derived from an ability to tweak specific laws of the physical world rather than from a broader ability to manipulate reality. However, within their windows of power spellcasters can be extremely versatile. Players of spellcasters will be allowed to create their own spells with Gamemaster approval as long as those spells realistically fall within the powers controlled by their characters. Furthermore, if a spellcaster can justify a use of their powers on the fly, that use will most likely be permitted. Further balancing will be done as the game progresses.