|Support||Cleric||Cleric||drop one of: stealthy, clever, surprise attack|
|Magical||Magic-User||Magic-User||scrolls, partial spells (tweakable spell list, prep, casting)|
|Turning||Cleric||Cleric||limited target, theme|
The explanation: If your class resembles a combo of two classes, look up each and choose the highest experience of the two and the lowest hit dice of the two. You also get some, but not all, of the abilities of each class: a Fighter/Thief combo would not have the full selection of weapons and armor that the Fighter has, nor would it have all three of the classic Thief skills.
If you want a combo of three classes: sorry. I do not approve. Try making a combo of two classes and switching to a third using the standard rules. If you want a class that's really one of the core classes, but with a change of theme, just change the theme of the class ability.
Explanation of the class abilities:
Combat: a full Fighter can use any weapons or armor. A Combat combo must drop one weapon class (one-hand meleé, two-hand melée, pole, ranged) and reduce armor to Leather (or None, for Combat+Magical.) Alternately, allow any armor, but impose an additional restriction on weapons (drop two weapon classes, or drop one class and add a broad restriction on edged weapons, or iron/steel weapons, etc.)
Support: a full Thief has stealthy abilities (move silent, hide in shadows, pick pocket, or detect a stealthy enemy with hear noise,) clever abilities (remove traps, open locks, climb otherwise unclimbable surface, read language or scroll,) and extra damage from a surprise attack. Drop one of these three when combining Support with another class to create a new class. Also, you can adjust or replace one or both of the remaining abilities to create a class equivalent to the Thief, but with a different focus (example: replace remove traps/open locks with create/modify device for a Tinkerer, replace surprise attack with appraisal for a Merchant.)
Magical: a full Magic-User has one spell list, a method for prepping (memorizing) and casting spells, and can make magic-items, including consumable magical items like scrolls and potions. A Magical combo either has no spells to start, but can learn any spell and create one kind of consumable magical items to cast them, or has limited casting ability (prep half as many spells.) Magical combos are also limited to spells that match a given theme, like illusion/charm spells or necromantic spells. Either Magical combos or full Magic-Users can be tweaked to create new magical types by swapping spell lists (Magic-User, Cleric, Druid, Illusionist, other,) changing prep method (memorization from books, asking spirits or a familiar, meditating in a specific location,) and/or changing casting rules (removing some restrictions while adding others, as in the Mesmerist class.)
Turning: The mechanic targets a specific type of creature it can influence (spirits/undead, animals, people, conjured monsters, weather) and has a specific theme for effects it can duplicate (healing/protection, charm, illusion, death, conjuration.) Change either or both for more variety.
... Now, what I'm thinking about in terms of "random classes" is some kind of roll to determine what the target or theme of the turning mechanic, spell list, or support ability is. But I'm going to have to mull over how to do this to meet John Oliphant's request. This may take a couple days.