I have the Magic Book, copies of some other d100 games with magic in them, and so on. I'm wondering about adding some new spells specifically if I run something -- things that will hopefully surprise players and people who read about them. But I don't want to go overboard in terms of spell power either -- I want these to by things a PC can cast (if she can learn them) without ecxhansting all their Magic Points in one shot and without totally upstaging the rest of the party.
Example: I want to be able to enchant a blade with Elemental Sharpness so that it can cut through any inanimate material. Things like pesky knots of the Gordian variety, reinforced wood-and-steel doors, obscene idols to the Unhallowed Ones, and so on. But the knife or whatever cannot penetrate living material at all, and does no damage to living things in combat from the edge (it would probably still leave a thin welt if it struck exposed flesh, but it wouldn't cut or penetrate the skin). You could cut a steak with it, but not a live cow. The spell would be of limited duration -- you might get one or two cracks at your slicing, but after that it either goes back to being a normal blade or becomes useless (losing its edge altogether, until you have the chance to go see a weaponsmith to get it sharpened again). In an extreme case the weapon could be utterly destroyed when the spell ends, shattering into a million pieces or crumbling to dust.
Now in a points-based system like Hero modeling this is a relatively easy collection of advantages and drawbacks that affect the spell's point total. There is no such guidance in most BRP fantasy settings or games. I'm wondering about things like the MP cost to cast, the number of spell levels it would take up, and so on.
It would, of course, function differently if it were a Divine spell as opposed to a Sorcery.