Elemental interactions

Planar interaction

—The infinite light and the before often fuse and stir. Wherever this occurs, their fusion becomes a wellspring of creation, a plasmatic broth of spirit, soul, light, and heat. The infinite dark and the after often fuse in a similar fashion to form oblivion. All things except reapers are quickly dismantled and erased from existence. Reapers are strangely able to predict oblivion and avoid it, sheparding souls around and away from it

Dual elemental users

—Occasionally people are born with two elemental abilities. Greater numbers are exceptionally rare, and no formal training exists for them. Opposite plane. The most common category of dual user is one which can use opposite elements in the same way, those being fire & ice, light & dark, birth & undeath, and life & corruption.
—Fire & ice users are commonly referred to as wind mages, because they are not confined to stirring wind up or cooling it down, and may control it more naturally by using fire and ice in unison. They are also rarely called water mages for a similar reason, however this title is more commonly attributed to ice & light users.
—Light & dark users are often the first to be offered the title of priest, for their ability to use light magic with no drawbacks, or at least the ability to rectify any problems that might arise. They also uniquely gain the ability to use illusion magic, but illusion mages are disqualified from becoming priests.
—Birth & undeath users may be called spirit mages, however they are thoroughly dissuaded from ever learning birth magic, as they may taint the before with dead souls. Besides this, their contributions are mainly a result of being able to do both types, but never at the same time.
—Life & corruption users may alter and reform spirits and souls in a variety of unnatural ways. They can shuffle spirit energy into and out of golems in order to produce extremely powerful guardians, or take control of existing golems. Sometimes they may help birth users recover from disorders of the soul, among other things.

Opposite manner

—The next largest category of dual user consists of those who can engage fully with exactly one other plane. Those four types are: fire & light, ice & dark, life & birth, corruption & undeath.
—Fire & light users - (any ideas?)
—Ice & dark users - (any ideas?)
—Life & birth users - (any ideas?)
—Corruption & undeath users are notably able to control and contain the souls of the dead, and are preferred over simple undeath users.

Notable minority combinations

—Fire & dark users are capable of fighting back against the spirits of the infinite dark, and may reliably perform dark healing rituals, which are mostly the same as light healing rituas, but in a dark and silent room instead of a very bright one. Like dark users, they may make use of dark gems to make the ritual that much safer.
—Ice & light users are capable of a lesser degree of wind and water manipulation to fire & ice users, and more often take on the title of water mage, for water's association with healing and tranquility.