One of the things I'm trying to do is to create mechanics for "magical pollution". I'm not sure whether it will consist of higher failure rates for people in "polluted" areas, random Fortean effects, higher incidence of magically altered and/or magic using monsters, or what. But I really want to at least have the option to make using magic something you just don't do casually, because there are consequences to be considered. Everything has a price, magic use should be no exception.
I've had the best success with this using the Law of Conservation of Energy. Casting a spell means the energy is taken from elsewhere within the system, not always for the best. I did not create tables but depended on the power of GM fiat. The over all result was people did not trust magic users and even more, resented them because they selfishly ruined every thing. Now have an enemy attack that can only be stopped via use of magic, and you have a fun setting were the hros are needed but despised. It is not a setting enviroment for all players (he said kindly, lol).
