Arcanists are perhaps the most unique spellcasters. They actually craft their own spells based on spell effects (magic school of Arcane). The gods have bestowed extra laws in the universe that can be harnessed and controlled by the Arcanists. For example, there are area effects, single targets, instant, fired in a line, touch based, etc. There's various effects like cold, ice, heat, fire, acid, electric, etc. The Arcanists decide all of these factors, and name their spell appropriately.
As an added bonus, Arcanists develop increased levels of magic resistance over time because of their constant manipulation of magic.