Magic 

The way magic is handled is probably the most important difference between S&S campaigns and normal D20 fantasy campaigns. In S&S tales the focus tends to be on the sword-wielders. Magic is just not that common. Worlds tend to bear a fairly close resemblance to our own in the ancient or medieval period and magic does not do a great deal to affect the social structure. There are no shops that sell magic items, and magicians are rarely for hire. Mostly they are shunned by the masses who (for the most part quite rightly) fear them. When it’s used magic is usually enormously tiring and mages rarely cast a great number of combat spells. They normally prefer to work behind the scenes and favour summonings to work their will from a distance. In many worlds just drawing on the forces of magic seems to have a warping effect on the body and psyche. There is usually an atmosphere of horror associated with magic.

The rules given here try to reinforce all of this. Probably the most important concept in S&S magic is that it always comes at a very high price. S&S magicians using some of these options may not seem very powerful when compared to a standard D&D wizard. This is quite deliberate. It reflects the genre. It should also be remembered that there is one balancing factor; the relative uncommonness of magic means that there are few people who can deal with it. Society as a whole is normally not as well prepared to deal with its magicians as it is in a more standard campaign.

Spellcasting Fatigue. 

Spellcasting is extremely physically draining for the caster. Every time you cast a spell you must make a spell fatigue roll. This is a fortitude saving throw against DC 10 + the level of the spell you are casting. If you fail this saving throw, you are fatigued. If you fail the saving throw when you are fatigued you become exhausted. Exhausted characters cannot cast spells. Fatigue and exhaustion are recovered from in the usual manner. If you fumble a spell fatigue roll, and are not fatigued you become fatigued and must immediately make another spell fatigue roll at the same DC as the first.

The Endurance feat does NOT give you a bonus to spell fatigue rolls.

Casting spells counts as a strenuous action for purposes of feats such as diehard.

Variant. If the DM allows you can cast spells while you are exhausted but to do so you must make your spell fatigue roll before you cast the spell. If you fail the spell does not go off and you are stunned for d4 rounds. The spell slot is lost.

Why? In the source material spellcasting is almost always extremely physically draining which is why this rule should probably always be in force in an S&S campaign. Anything that reduces fatigue should be looked upon with suspicion by the DM. This is particularly so if you are using the spell slot magic version of the sorcerer which is in many ways more powerful than its SRD counterpart when the trend should be to make it less powerful. Potions and other one-shot devices that the DM has some control over the provision and disposal of are not so bad. Spells are the real problem. If you choose to use one of the variants that allow such spells to become available to PCs you should be very careful.

There are several ways of dealing with them. You could simply ban all spells and effects that reduce fatigue. Or you could assume that the fatigue caused by spell use is so deep that methods that remove normal fatigue simply don’t work with it. Or you can assume that such spells are very draining and can only be cast by people who are not fatigued and automatically cause a level of fatigue to their caster