Since COIL will not be a d20 product when I release it, I am brainstorming magic system ideas.
At present, I have a dice mechanic that supports five, at tops six, different magic styles.
In order to capture the level of fear and trepidation in the game I am thinking that Divination Magic is prevalent and the easiest magic to cast. It is everywhere in the city and allows people to watch everyone's movement.
Wards are also everywhere (a second kind of magic).
Enchantments are a useful tool of the "church" and internal negotiations of the guilds.
Lightning is the offensive magic of the realm, used to keep others in line. The guilds have learned to shape it as well, creating walls of lightning. Because the city would be ravaged by fire, magical fire is outlawed and punished by death.
Finally, there is shadow magic, guarded and protected from other "lower" classes of mages. It is a tool of assassins and mages that come into the homes of those who oppose the state.