From Compendium of Worldly Lore
Wizards who gain power by creating a circle which can augment their caster level and make them extremely powerful. They also gain more spell power.
Role: Spell DPS
Characteristics: A wizard that eventually assembles a circle of others around them
Source: Dungeon Master's Guide
Game Rule Information
The Red Wizard has the following game statistics.
Abilities: Whatever your casting stat is, Intelligence for skill points,
Alignment: Any Nongood
Hit Die: d4
Starting Gold: N/A
Class Skills
The Red Wizard's class skills are Bluff (Cha), Concentration (Con), Craft (Int), Intimidate (Cha), Knowledge (all skills taken individually) (Int), Listen (Wis), Profession (Wis), Search (Int), Spellcraft (Int), and Spot (Wis)
Skill Points at 1st Level: (2 + Int modifier) × 4
Skill Points at Each Additional Level: 2 + Int modifier
Class Features
All of the following are class features of the Red Wizard.
Weapon and Armor Proficiency: A Red Wizard is proficient with whatever they were already proficient with.
Spells per Day: A Red Wizard’s training focuses on arcane spells. Thus, when a new Red Wizard level is gained, the character gains new spells per day as if he had also gained a level in whatever arcane spellcasting class he belonged to before he added the prestige class. He does not, however, gain any other benefit a character of that class would have gained (bonus metamagic or item creation feats, bard or assassin abilities, and so on). This essentially means that he adds the level of Red Wizard to the level of whatever other arcane spellcasting class the character has, then determines spells per day and caster level accordingly.
If a character had more than one arcane spellcasting class before he became a Red Wizard, he must decide to which class he adds each level of Red Wizard for the purpose of determining spells per day.
Enhanced Specialization: Upon becoming a Red Wizard, a character increases his devotion to his wizard school of specialization. In exchange for this, the Red Wizard must sacrifice study in one or more schools. The Red Wizard must choose an additional prohibited school or schools using the rules in the Player’s Handbook. He can never again learn spells from those prohibited schools. He cannot choose the same prohibited schools he chose as a 1st-level wizard. He can still use the prohibited spells he knew prior to becoming a Red Wizard, including using items that are activated by spell completion or spell trigger.
For example, Ghorus Toth is specialized in the school of transmutation. His prohibited schools are abjuration and enchantment. When he becomes a Red Wizard, he must choose one other prohibited school. He decides to select conjuration as his additional prohibited school.
Specialist Defense: A Red Wizard gains a bonus on saving throws against spells from his specialist school. This bonus starts at +1 and increases at higher levels.
Spell Power: At 2nd level, a Red Wizard gains a bonus that increases his effective caster level for purposes of determining level-dependent spell variables and for caster level checks. The bonus starts at +1 and increases at higher levels, as shown. This ability stacks with other spell power benefits that affect spells from the Red Wizard’s specialist school.
Bonus Feat: At 5th level, a Red Wizard gains a bonus feat, which must be either an item creation feat, a metamagic feat, or the Spell Mastery feat.
Circle Leader: At 5th level, a Red Wizard gains the ability to become a circle leader, who is the focus person for Red Wizard circle magic.
Scribe Tattoo: At 7th level, a Red Wizard gains the ability to place the Thayan wizards’ magic tattoos upon willing and qualified novices and inducting them into his circle.
Great Circle Leader: A 10th-level Red Wizard can be the leader of a great circle, which can have up to nine other participants instead of just five.