Old name: Magic-User
Description: Warlocks are men and women who seek occult knowledge in a never-ending quest for personal power. Some attempt to use white magic to beat back the darkness, while others have no qualms over battering their souls away for arcane secrets.
Inspirations: Dion Fortune's The Demon Lover, H. P. Lovecraft's “The Dunwich Horror”
Changes: 1d6 Hit Points per level. Many spells with receive a heavy re-flavoring to be more in-line with the genre. Expect many of those flashier staples (Fireball, Magic Missile, etc.) to become more subtle and more darkly hued. For example, while the usual Fly spell is pretty lame as-is, if it becomes a spell that can only be used to fly if that character rides a broom Walpurgis Nacht-style, then we might be in business.
Also, it's a very flavorful thing to give your warlock a “theme” that colors his or her use of magic. For example, if your warlock uses “shadow magic,” then we can give all of her spells subtle (or not-so-subtle) trappings and effects that reflect her style of magic. Some possible themes: diabolic pacts, spectral magic, blood magic, astrological magic, fey enchantment, Lovecraftian magic of madness, voodoo, etc.
Old name: Illusionist
Description: Mesmerists are cunning men and women who have mastered the arts of mind, control, suggestion, and illusion.
Inspirations: Charles Brockden Brown's Wieland, George du Maurier's Trilby
Changes: 1d6 Hit Points per level. See Warlock for changes in the way spells are flavored.
Old name: Thief
Description: Bandits are outlaws and wolf's heads who skirt the laws of enlightened civilization; they may be ruffians and highwaymen who care little for else besides their own gain, or they might be rebels who strike back against an oppressive regime.
Inspirations: Ann Radcliffe's The Mysteries of Udolfo, Percy Shelley's Zastrozzi
Changes: 1d6 Hit Points per level. A bandit gets a +10% bonus to the Pick Locks, Find and Remove Traps, Pick Pockets, Move Silently, and Hide in Shadows special abilities.
Old Name: Assassin
Description: Assassins are experts in the art of dealing death; some assassins are merely cold-blooded killers-for-hire, others are principled murderers seeking to avenge a great wrong.
Inspirations: Ann Radcliffe's The Italian, Edgar Allan Poe's “The Cask of Amontillado”
Changes: 1d6 Hit Points per level. Assassin's get all thief abilities as if they were a thief of the same level; they do not get bonuses to these abilities as a bandit does.
One thing you'll note: no monks.