Allow me to elaborate on the classes with my best guesses, based on descriptions in old dragons, and some of these former classes were mentioned as possible professions in MYTHUS, save for the Jester.
From what little I remember from this and Dragon, the Savant was mentioned to have powers to overcome some of the altered magics of other planes, and I would assume they were like mages, but more akin to a combination of 1st Edition Sage, Specialist Wizard (3e) Diviner, and 3e Expert or Prestige class Loremaster. Their abilities would likely deal with knowlege rather than evocations, so they might be better at things like Divination and Abjuration or even Conjuration spells than the typical mage. The 1st Edition Derro "savants" in 1e MM2 might also be akin to what the class would have been.
I assume mystics had more yoga like powers--Gary had mentioned that in playtest "mystics rated the lowest, since nobody had them at #1". Whatever that means. Maybe powers were randomly generated? I assume this involves communing and inner psychic powers and astral projection. Like Gary said, Divine Divination and Fortune-Telling would also be part of this class. Holy Men and hermits might be the way to go here.
Mountebanks--well, if we think Hop the Savant having those powers, it might mean a thief or rouge with powers to create potions--some fake, some real, and probably some "hedge-mage" types of powers. If we were going by the 3e, a mountebank template might be a rogue specializing in using magic items, con-games, and potion brewing, with maybe a bit of 3e sorceror or 1e Illusionist. (Sorry, best way to describe the class). They probably are seen as "pretenders" to magic--having just enough to get by, but a real mage or wizard would probably scoff at them.
Jesters--Probably similar to the bard, but it probably was akin to the mythus skill of buffonerry, which combines joke telling (think of something that either humiliates or puts a victim into a reckless rage, or incites a riot), with pranks (akin to setting traps, or getting hit with a pie or slipping on a banana peel), maybe some illusion or enchantment magic as well.
That's all I can surmise.
![:]](http://www.enworld.org/forum/images/smilies/devious.png "Devious :]")
