Another question as well.. how does fast cast defenses actually WORK?
We always thought that.. say, if a pilum was coming your way, you could make a terram barrier in the way as a fast cast defense.. but suddenly I doubt it..
For a start, why would you need to know the form of the spell incoming and such?.. and compare to level rather than penetration. .. I suddenly came under the impression that it's more like countermagic.. you're not trying to make a barrier.. as that is often impossible with targetted spells.. you're instead actually using magic to degrade and just make the spell flop out of existence before it reaches you.. .. I think that works better really.. but.. .. again, unsure.. it never actually -specifies- such things.
Set aside this particular doubt. It does you no good
I advise to let the two words before "a fast cast defense with half the level..." guide you . These word are "In general" let reason be your arbitrating factor. there are no more specifics because there are too many variables to be more specific.
You need the form to figure out what the other caster is doing. You can fast cast any spont spell or spell mastered for fast casting as a reaction to an event. So if you've mastered conjuration of the obese dromedary for fast casting you can fast cast it as a reaction to an incoming spell regardless of whether or not you know what the spell is.
My guess is that learning the form and getting half of the attacking spell's level are specifically there to give the SG some rough guidelines and, as you said, specifically allow a caster to unweave an incoming spell because , lets face it, how cool is that?
You can look at it like this...A magi has a casting total of 50, he cast a level 25 spell creating a ball of yarn that flys out and strikes the target. 25 of his total is just added force to his throw, if you unravel the ball it wont matter how hard it's thrown.
Same magi creates a level 40 knit sweater, it's more difficult to unweave.
There is alot that can add to penetration that has nothing to do with your skill in crafting the spell. this just adds to the force of your throw, not how well you wove the spell.
Yes Agnar, but the problem is.. that's an argument that you're disrupting/countering the spell.. because if you were just making a big wall of stone in the way to block it, surely penetration would be a factor instead?
But when you spont, you burn fatigue, when you cast a mastered spell (even fast cast), you don't...
Seems a long run better option..though sometimes you don't have a choice.
No, you need a total of 20. I think you've got something mixed about the sponting rules.
The rules are in the fast cast section I think that they are as you suggest but my memory could be wrong.
Because you need to burn fatigue to counterspell (unless your total before die roll is 50 or more).
Becuase getting a casting total of 20 to counter a level 20 spell isn't too tough but acquiring a casting total of 40 to counter a level forty spell is darn hard.
Because unravling the fabric of form can be used for more than counterspelling, in fact the spell in the core book isn't designed for counterspelling and can't be used for it unless you master it for fast casting.
Because they might multicast and a long duration unravling the fabric spell could stop it more easily than a huge counter spell.
Because getting more than one spell off per round is very difficult and putting up a long duration unravling spell could allow you to make your one spell something other than a defensive one.