Illusionists

The illusionist is an example of a specialist. The description of the illusionist given here can be used as a guide for creating wizards specializing in other magical schools.
First, the school of illusion is a very demanding field of study. To specialize as an illusionist, a wizard needs a Dexterity score of at least 16.
An illusionist who has an Intelligence of 16 or more gains a 10 percent bonus to the experience points he earns.
Because the illusionist knows far more about illusions than the standard wizard, he is allowed a +1 bonus when rolling saving throws against illusions; other characters suffer a -1 penalty when rolling saving throws against his illusions. (These modifiers apply only if the spell allows a saving throw.)
Through the course of his studies, the illusionist has become adept at memorizing illusion spells (though it is still an arduous process). He can memorize an extra illusion spell at each spell level. Thus as a 1st-level caster he can memorize two spells, although at least one of these must be an illusion spell.
Later, when he begins to research new spells for his collection, he finds it easier to devise new illusion spells to fill specialized needs. Reæarch in other schools is harder and more time consuming for him.
Finally, the intense study of illusion magic prevents the character from mastering the other classes of spells that are totally alien to the illusion school (those diametrically opposite illusion on the diagram). Thus, the illusionist cannot learn spells from the schools of necromancy, invocation/evocation, or abjuration.
As an example, consider Joinville the illusionist. He has an Intelligence score of 15. In the course of his travels he captures an enemy wizard's spell book that contains an improved invisibility spell, a continual light spell, and a fireball spell, none of which are in Joinville's spell book. He has an 80 percent chance to learn the improved invisibility spell. Continual light is an alteration spell, however, so his chance to learn it is only 50 percent (consult Table 4:Intelligence to see where these figures come from). He cannot learn the fireball spell, or even transcribe it into his spell book, because it is an evocation spell.

Ability Requirements: Dexterity 16
Prime Requisite: Intelligence
Races Allowed: Human, Gnome