Summary of Dungeon Master's Guide Prestige Classes in the Three Worlds
Most of the prestige classes found in the Dungeon Master's Guide are generally available in the Three Worlds campaign setting. In many cases the training needed to obtain levels in these classes can be obtained via one of the many groups and organizations found in the setting. In most cases, these prestige classes are not exclusive to any one organization or mentor, but can potentially be learned from a variety of sources.
Arcane Archer: As there are no elves or half-elves in the Three Worlds campaign, the arcane archer prestige class is one of the few such classes found in the Dungeon Master's Guide that is not available.
Arcane Trickster: Arcane tricksters can be found almost anywhere there are thieves' guilds. Although members of any race can become arcane tricksters, the vast majority are gnomes or halflings, with many of the various merchant houses and pirate clans of halflings having a number of such individuals in their ranks. Among the Collegium, many arcane tricksters take the role of spies and special operatives.
Archmage: To become an archmage one must obtain training directly from an existing archmage. The most famous archmages in the Freeholds are Dallen and Mannan. Although this has never been confirmed, it is widely believed that Leannan of Dewintir is also an archmage. Members of the Collegium and the Leucadian Brotherhood would have access to at least one potential mentor through their organization.
Assassin: As an exclusively evil class, the assassin prestige class is not generally available to player characters in the Three Worlds. Groups of assassins may be found throughout the Three Worlds, often associated with the cults devoted to Gangyn, Kivutar, and Vassatar, although assassins may be found in the service of almost all of the Lords of Hell. The vast Gemelas criminal network based in Castille also relies upon a large cadre of assassins to enforce its will.
Blackguard: Like assassins, the blackguard is an exclusively evil class and is therefore not generally available to player characters in the Three Worlds. Blackguards are found among all of the devotees of the Lords of Hell, serving their priesthoods as lieutenants, champions, and war leaders. Blackguards are especially common among the cults of Belial, Darmas, Khil, and Tuni.
Dragon Disciple: As dragon disciples are associated with the Great Dragons, they are most often found among the Cult of the Dragon in the Dekkulde Islands, but there are a number located in the Gorovlic Isles or on Croesfan Island due to the close proximity of the dragon Hraegnscaga in the Pirsh'tas Islands.
Duelist: Duelists can be found almost anywhere, although for obvious reasons, many duelists are found in the Gorovlic Islands among the pirate clans and merchant houses found there. Many fighting schools in Enselm teach the elements of this class, but teachers may be found anywhere lightly armored warriors are in demand.
Dwarven Defender: Members of the dwarven defender class can be found anywhere there are dwarves, but they are most common in Steinigreich, which is where dwarven legend says that the teachings and methods of this class originated. Many members of the Order of the Shield are also members of this class, with dwarven members of the Order routinely alternating between this and the prestige paladin class.
Eldritch Knight: Eldritch knights can be found anywhere there are warriors and mages, and as one might expect, many members of this class are gnomes or avari. Eldritch knights are also often associated with Dewintir, as they form the backbone of that nation's armies. Eldritch knights do not, however, exclusively hail from Dewintir and most arcane organizations have at least a handful of members who dabble in martial matters. In the Freeholds, many eldritch knights hail from Dyfed, and there are many members of this class among the Wardens and Warknights of the Council. In addition, members of this class are often frequently found among the cults devoted to Woda, Ishii, Füllar, and Vali.
Hierophant: Hierophants may be found among nearly every faith or circle of druids in the Three Worlds.
Horizon Walker: I am currently unsure where the horizon walker class would fit in the Three Worlds campaign setting, and as a result, this prestige class is not available for player characters.
Loremaster: In the Three Worlds, loremasters are most often associated with the deities Woda and Füllar, although many devotees of Ishii also take up this calling and very rarely, devotees of Vassatar. Loremasters are also associated with the great libraries and centers of learning in the Three Worlds, with the most famous being Mannan and his followers who study at his fortress on Ynys Mon.
Mystic Theurge: As a class dedicated to the merger of divine and arcane magic, it is natural that many mystic theurges may be found among the adherents of the cults of Woda, Füllar, and Ishii, but they can be found among the ranks of almost every faith in the Three Worlds. Although rarer, there are those among some druidic circles who believe that the only way to understand and honor the power of y'Grym is to combine divine knowledge with arcane power. Notably, there are many mystic theurges found among the ranks of the Wardens of the Council, as the versatility has proved extremely useful in many situations.
Red Wizard: The Red Wizards are the ruling elite of Valentia. They were once one of the most powerful of the many factions vying for control of Yle, but since the mystical destruction of that land, they have been reduced to a remnant of their former numbers. The Red Wizards have made clear that they are not content to rule a single isolated island in the Sea of Fear, and their tendrils of influence extend throughout Midrun and beyond. For a player character to become a member of the Red Wizards in the Three Worlds campaign setting would be unusual, although not necessarily impossible.
Shadowdancer: Until a few centuries ago, shadowdancers were fairly common in the Three Worlds, with many finding their home among the Sang-Nuit in Enselm. Then, for reasons unknown, the Collegium turned on the practitioners of this art and embarked upon a ruthless campaign of extermination apparently aimed at destroying anyone who had any knowledge of the shadowdancing way. Now shadowdancers are rare, and conceal their abilities from anyone who does not have their complete trust.
Thaumaturge: Thaumaturges are found among nearly every priesthood in the Three Worlds, but are most common among the devotees of Caire, Hler, Wünd, and Yng. Among the cults devoted to the various Lords of Hell, Thaumaturges are often found among the ranks of those serving Belial, Gangyn, Halpas, and Ishii.