New campaign looking for feedback.

[Goodlun]

Well its coming about time for a new campaign.
For this campaign I am thinking of introducing a campaign quality where to regain SP the magic user has to drink some horrible concoction that one makes them have to pass a fortitude save or(not sure yet), two contains blood from a naturally magical creature.  Thinking of maybe having the potion restore maybe a 1/4 of the xp value of said creature.  Also this would not stack so to recover 20 sp one would actually need the blood of an 80xp creature. Not say 2 40xp. 
This is to deliberately make magic rare and special, and in part to help with the whole economics of magic vs technology. 
In the case of a PC being a mage(thinking about nixing that idea as a starting class) I might be willing to let them inherently be able to cast with out the potion if they take a species feat. 
This is going to be a human centric campaign probably with a fantasy industrial age feel to it, with the wonder if magic is even real to start with.
All ideas and suggestions welcome.

[Mister Andersen]

Unless this is purely descriptive fluff the cost of which is assumed to be covered by the prudence mechanics, I dislike that idea intensely. Not least because it throws game balance horribly out of whack: no one else is being hit with what amounts to a tax for a class ability.

Something like that is better applied as a gate-keeper for acquiring new spells: a spell can be looked at essentially as no different from a new or upgraded weapon

[paddyfool]

Perhaps you could do it like this?

Campaign Quality: Difficult Magic

New Elixir: Blood draft; 50s; negates the Difficult Magic penalty for the next spell that you cast.

(That way, it isn't absolutely essential for casting, but definitely useful; I'd have to check the rules on crafting elixirs to be sure this is appropriate, however).

[Desertpuma]

Another thing you could do once Spellbound comes out is remove the Mage and allow only the classes that are beholden to a school. With the training comes a way to focus yourself through Resolve so you don't need the elixir.

[Nova]

 Don't forget that the bigger, less momentary magics do have costs that go beyond just a few silver already. Anything with a preparation cost is effectively either so expensive or abstract in its requirements that you can't even fish out a few silver, but instead have to grease hands, call in favors, and maybe get zoning authorisation or whatnot.

 Problem with the potion is that SP for the most part is only a factor in short-term fights, resulting, without a party doing a lot of the work for them (and they may be less than happy given you're not using SP to buff them up for the job) in a zero-sum game fairly often.

 Would you be locking out the mage core ability too? if so what are you going to give them to make up for such a fairly heavy loss?

 Just to be clear on mages: Their power in FC outside of those prep-cost spells isn't so great as to invalidate other classes (as they do in 3.x and pathfinder). Combat-wise plenty end up with very similar capabilities, if a little less AoE, and in fact the normal-weapons types can dish out twice the damage to one or two targets at a time with a far greater chance of going straight to wounds.

 On the whole, Half SP regained per scene combined with Difficult Magic would probably do the job a lot better, without making it almost pointless to roll a mage. That +5 DC turns "you can somewhat-to-fairly reliably (we're looking at 1-5ish for rolls that fail, depending on how focused on his casting ability to detriment of all else the character is) cast spells of the highest level currently available" into "somewhere about half the time it works". The doubled casting time is almost fatal on its own, atop it all.

[Goodlun]

I was planing on locking out the mage class  either all together or more likely at least for the 1st few levels Planing on treating it more like a expert class. 
The idea being magic won't play a central role but I do want it around and to be powerful but very limited in deployment.

[Desertpuma]

Another way to do it is allow the Mage class but one cannot multiclass out of it and the xp levels to progress in it are x3 or x4 or x5. This allows the class but also restricts the growth of someone in it.

[Nova]

Another way to do it is allow the Mage class but one cannot multiclass out of it and the xp levels to progress in it are x3 or x4 or x5. This allows the class but also restricts the growth of someone in it.

I really would not advise that.
Goodlun's idea on "expert class" isn't too bad. If you want it to be powerful, perhaps "Potent Magic" with difficult and that "regain less SP per scene" would do the trick.

Mages in FC start with 0 level spells, not first, so 5-15 being the limit, they will never see levels 8 and 9. That means no Time Stop (its not as bad as in D&D don't worry), none of the Category 5 spell versions, no Iron Body, and so on. 7's the limit at the very endgame.

 30SP per scene plus the lack of the core ability means very few spells a scene, but fact is, a lot of these spells are often loaded by nonspellcasters on magic items. Those may be a more important thing to keep tabs on and/or limit than the spellcasters themselves, if you go that way. Again though, Its important to stress the differences between Fantasy Craft and other similar systems, since magic was redone from the ground up and actually balanced for once.

[Goodlun]

Its important to stress the differences between Fantasy Craft and other similar systems, since magic was redone from the ground up and actually balanced for once.

This is very true.  I am contemplating a very low magic campaign very few if any magic items hardly any spell casters.  Truly rare gifts indeed.  I am looking at it as a lost art something that was once prevalent but has fallen aside.  I would like the mechanics to justify this. 
Thinking of an industrial age campaign where people are still very superstitious but for the most part do not out right believe in "magic" per say.

[paddyfool]

I would say that your idea of having the Mage as an expert class would be a good one, in that case.  Not sure what you'd best take from the first 14 levels to make a good 10-level progression, but it should be pretty doable.

[Desertpuma]

You could also make Mages like the Sith. You know: one master, one student. Train in secret. Generally thought of as evil or misguided.

The advantage this gives you is that players wanting to be Mages have to seek out a teacher. So they have to find a solo Mage who is willing to instruct them.

[ludomastro]

Or if you wish to carry out the Sith metaphor for a bit: they'll need to find an apprentice willing to kill his master.