In the system I'm designing, spellcasting is a skill. It effectively gives you the the ability to use rituals and some cantrip-like effects. When you cast a spell, you roll your skill. The margin of success or failure may make a difference - degrees of success can usually be spent, after the roll, on things like duration. You can buy additional sets of spells as feats. For instance (and I'm making this up as I go along), the feat Fire Magic I might let you use spellcasting to attack a single individual (and maybe a small area) with fire, protect yourself (and maybe others) from fire, start fires, and cause fires to flare up/die down.
I don't want to use a Vancian fire&forget system or import a spell point system. What I do want is something that will keep a spellcaster from casting the same spell over and over again. In combat, it might be nice for the fire mage to occasionally do something other than attack someone with fire, but that isn't my primary concern. I'm more worried about down time. Consider the fire mage who wants to protect himself from fire. What can be done to prevent him from rolling his spellcasting until he gets an incredibly good result?
Currently, I'm considering three options:
- Diminishing returns: If you cast a spell with a duration, any subsequent uses of that spell on the same target are made with a cumulative penalty. I'd have to play with the notion of duration here, since some spells that I'd want to include in this - like healing spells - are usually considered instantaneous.
- Extra cost: If you cast the same spell twice in a row, the second use costs a Fate Point (a fairly valuable meta-resource). The problem here is what "twice in a row" means. I don't want the healer to heal someone, shoot a fireball into the air, and heal that person again. That's silly.
- Fatigue/health cost: I'm generally not a fan of this, but the system I'm working with allows for some flexibility in interpreting damage. It will probably be an option for failed spells... and, coupled with option 1, that might be a significant deterrent.