I went back and forth on what to do about magic users a bit, given the artificer class and another magic-using class I'll be adding soon; but in the end I came back to a pretty stock-standard version of the existing class... with a few significant, embedded house rules. You'll note the XP values differ from the norm, I used the guidelines from here, counting Class Abilities as Specials I & II as per these rules.
The biggest differences between magic users in other games/ campaigns and those Beneath the Broken Moon involve my house rules on orders and master's background and the spell selection. As there are no clerics nor druids in my world, the magic user is the spellcasting class. Magic users are the theoretical and experimental physicists of magic... they understand through intuition and arduous study the fundamental underpinnings of reality and have learned/ developed the formulas that allow one to bend and twist it through rigorous experimentation. Whichever Order a mage belongs to will dictate beginning spells and spells selected as one progresses thorough the levels, but a magic user is able to learn, memorize and cast ANY spell that they are of sufficient level to cast.
I'll most likely be using the very excellent Libram Magica BFRPG supplement (free .pdf, found on that game's download page) for the length and breadth of spells but will need to create a unified spell list to eliminate duplicates and similar spells formerly allotted to separate classes as well as determine appropriate level designations where identical spells are different. I'm not looking forward to this task, so I can't say when I'll get around to it... soon though. Anyway, here it is...
Requirements: Int 9
Hit Die: 1d4
Save As: Magic User
To Hit As: Magic User
Weapon Proficiencies: Staff, sling, dagger, club
Non-Proficiency Penalty: -5
Armor: See below
Level Experience Points Class Abilities
1 0 Read Magic, Spellcasting, Research
5 19,600 Brew Potion
9 313,600 Craft Magic Items
20 1,881,600 Create Artifact
Read Magic & Spellcasting: In both BFRPG and my campaign, reading magic is a class ability and not a spell. Those that may read magic may learn and memorize spells as per the normal rules. Reading magical writing requires a bit more concentration than reading mundane texts, but beyond the added effort there are no special rules or stipulations at this time.
Magic users begin play with 1d4 spells and then must roll on the table here to see if this number is further augmented. My rules for magical orders are in play and can be found here and demonstrated here. As noted above, only a magic user's initial spell selection and those spells chosen when advancing levels are bound by the limitations of his or her Order. A magic user may learn, memorize and cast any spell.
Research: One of the skills that sets magic users apart from any other magic-using class is their ability to discover and/ or create spells via magical research. BFRPG has rules for this and I have a set of rules written up for my last campaign. One or the other will be in effect, to be determined before play begins. The broad strokes are what might be commonly understood by any reader by now: mages can spend time and money to discover and learn new spells.
Item Creation: Brewing potions, crafting arms, armor,
miscellaneous items, rings, wands staffs and rods are all accomplished under the guidelines and costs in time and money presented under Item Creation in BFRPG. Unlike artificers, magic users do not need plans nor reverse-engineering to create items. They must wait until 9th level to create anything other than a potion, yes, but at that time they are not restricted in the types of items they may create.
Craft Artifact: An artifact is subjectively defined as a
singularly unique and powerful magic item. A 20th level magic user is
capable of crafting such an item, but the way is arduous, expensive and
fraught with peril.
Armor: Nothing is preventing a mage from wearing armor, but it is not without risk. Rules here.