The Seers

Magic in Kytheria is well defined and studied, for the most part. Members of prestigious wizarding academies would certainly have you believe that those born with the Mark have plumbed the depths of what is possible through magic, and that any magic that can be performed with the proper set of symbols and utterances has been discovered with only a few permutations cropping up as 'new magic'. These academies are feared and sponsored by nations, and when rulers are not themselves among the Marked they most assuredly have a wizard in their employ.
Magic is not so easily constrained, however.
Those with the Mark draw their power from the Girdle of the Gods, high in the heavens. The power is discrete and able to be take myriad forms, often serving as what laypeople refer to as 'magic'. However, this artifice of the gods is exactly that, and in quiet apartments tucked away on busy streets, cottages at the edge of town, and occasionally remote huts in the middle of the wilderness, another form of practitioner toils away and serves as diviner, healer, and more for those who know how to ask. 'Seers', as they are collectively called across numerous languages (though other names, sometimes pejorative, are also used), access what they deem true magic: the fabric of life and fate itself. Unlike wizards who draw power into brute-force applications along very specific guidelines, the seer communes with the spirits, or gods, or dead, or all three, seeking their aid and knowledge. They also work their will upon the world around them, though some would say that they simply ask the little spirits in all things to intervene while others insist that it is willpower itself. Little debate occurs however, as in most places the Seers aren't meaningfully organized, with a master teaching an apprentice or three and leaving them to care for the community when the master departs. 
Divining the will of the gods, particularly those who control fate, is a specialty of the Seers. Wizards might cast a spell for a glimpse of the future, but it is always couched in riddles and the meaning often remains undiscovered until the event has come to pass. Seers commune directly though, enabling them to better apprehend the situation and intuit what the gods or spirits mean directly. Healing is also common, with various poultices and potions being known for a variety of problems, though if one can heal one also knows how to harm, and rumors of Seers offering curses and poisons is not without foundation.