Here's part 2, in which I make up a bunch of new features for custom classes. These are all home-brew.
New Skills, each rolled on a d6 and starting at 1-in-6 like other Specialist skills.
Medicine: On a successful Medicine roll (which takes a turn) you can do one of the following:
Provide first aid, raising a patient on 0 or less HP to 1 HP, so they're awake and not dying anymore.
Accelerate healing, so that the patient heals [the result on the d6] extra HP when they next sleep.
Diagnose a disease, poison, or other condition.Failing the Medicine roll deals 1 damage to the patient from the dubiously necessary medical procedures.
Swimming: Required to keep your head above water if you're encumbered or swimming in dangerous conditions, might also let you do tricky things underwater. Reduce your swimming chance by your encumbrance level; armour drags you down.
Leadership: A character with at least 2-in-6 in this skill can make a leadership check when first hiring a retainer. If it succeeds, add [the result on the d6] to the retainer's loyalty/morale, up to a maximum of 12.
Cryptography: Works like the Languages skill, except it applies to cracking codes (or devising new ones for a given purpose). A successful cryptography roll lets you read things like scrolls and spell-books without casting detect magic. Intelligence modifier applies.
Force Open Doors: you can put skill points into this. Strength modifier applies.
The following is an additional option for how you cast.
+500 to cast through an occult pact (see below).
The following are additional options for what spell list you use.
-100 A tightly limited spell list (see below for examples).
-400 A single spell. Probably something flexible like Summon.
The following are additional extras that a spell-caster might have.
-100 if spell casting requires a blood offering (spending HP equal to the spell's level).
-100 if you must spend a round ritually preparing to cast, before actually casting the spell.
The capacity to mimic the effect of a spell. Base cost is:
100 multiplied by the level of the spell. (IE a level 2 spell costs 200 XP, etc).
Allowing the spell to be cast once per day.
x2 if it can be cast once per hour.
x3 if it can be cast once per turn.
x4 if it can be cast at-will.
x½ if it can only be cast when the character reaches the same level a Magic User would need to be to first cast it (ignore for 1st level spells).
x½ if it requires significant materials (costly, rare, proscribed, taken from corpses, etc) to cast.
x½ if it can only be cast in specific circumstances (while on holy ground, if the caster is on half HP or less, in a well-stocked laboratory, etc).
So, the fighter is costed weirdly (hence the 'fighter tax'). If we're introducing homebrew, I'd have the fighter's bonus to hit cost only 200 XP, and then all by the book fighters get the following as well:
+300 to be able to Follow Through In Combat: whenever an attack drops an enemy, you can make another attack immediately. Can't make more of these bonus attacks per round per enemy.
The following are also home-brewed combat abilities:
+200 to add your level to all damage rolls.
+200 to be able to step in the way of an attack that would hit an ally next to you, taking the hit yourself instead. Diving in front of bullets, bodyguard-style.
+100 to grant +2 AC to those fighting to either side of you when you use the Parry combat option. Doesn't stack if multiple combatants use it, you dirty power-gamer.
Abilities you get because you're not even slightly human. Having these probably makes you chaotic (or, less commonly, lawful).
-50 if you must consume some problematic substance (either rare, expensive, harmful or socially taboo) substance each day or else take penalties as if starving. Examples include human blood, carrion, holy libations, or opium.
-50 if you are undead and thus vulnerable to all things that target undead.
-50 if some material does double damage to you, eg cold iron, silver, etc.
-50 if you are unusually flammable and take double damage from fire, heat, etc.
+150 if you do not require food & drink like mortals do.
+100 if you can breathe water just as well as air.
+100 if you cannot feel pain and must be physically hacked apart, making you immune to back-stabs.
+200 if you do not breathe at all.
+200 if you cannot suffer from diseases due to a lack of biological functions.
+400 if your form is amorphous and flexible, allowing you to pass through small gaps, shape your body oddly, and add your level to Wrestling rolls (if you don't do that already by adding your level to hit rolls)
+800 if you are totally intangible, able to pass through walls etc, immune to physical damage, and unable to touch, carry, or be touched by any physical item.
+100 to have an unarmed attack (bite, claws, etc) that does d6 damage. +50 for each dice size bigger the attack is (so d8 costs +150, etc).
Weird things you can learn to do.
+500 to be able to graft body parts onto a patient with a successful Medicine roll (see above). Doing so takes an hour, requires intact fresh body parts. The result depends on the body part grafted, but examples include extra limbs (allowing you to hold more stuff), extra eyes for 360 vision, organs from monsters granting powers the donor possessed, bony armour for extra AC, claws that increase the damage of unarmed attacks, etc.
+300 to be able to take detailed scientific notes, sketches, etc of unusual things you encounter, enough that scientists in the relevant field will pay for them as if they were treasure. Taking these notes requires an hour to work in and uninterrupted, safe access to the subject. Probably worth around 500 Silver, maybe more for the most unusual specimens. Could equally apply to a talented artist making paintings, a chronicler recording findings for a wealthy patron, etc.
+100 to be able to see twice as far in low-light conditions.
+200 if your unusual vitality lets you heal twice as fast as normal.
+100 to be more effective at some mundane task a (digging, navigation, etc). As a rule of thumb, as effective as your level +1 normal workers.
+100 to be able to perform the functions of some specialist retainer (such as an accountant, alchemist, armourer, etc).
+100 for each 100 silver or additional equipment you start out with.
-100 to start out with only a handful of equipment (perhaps a weapon and one other item, and d6 silver).
Casting through Occult Pacts
For when a character's spells are granted directly by the patronage of some otherworldly being.
The spell-caster starts out knowing only 1 spell from their relevant list. They learn an additional spell whenever they gain a level. The level of this spell is equivalent to the highest-level spell slot that a MU of their level gets access to. (So at 3rd and 4th level they get a Level 2 spell, at 5th and 6th level they get a Level 3 spell, etc).
To cast a spell, the spell-caster must roll a d12 and add their level: if the total is 13 or more, the spell succeeds. A roll of 1 always fails.
If the spell roll fails, the caster's patron requires something of them; some specific sacrifice, a mission to advance the patron's goals, setting up a shrine, proselytising, etc. The Referee determines what. The spell fails, and no further spells can be cast until the task is complete. Alternately, the patron might require their pawn to swear some oath (such as never bearing weapons, never harming spiders, etc); breaking this oath deals d6 damage per level to the character as they are smote, and prevents them casting spells at all for a day.
Tightly Limited Spell Lists
Probably want to only have 1-5 spells at each level. Some examples include:
Illusion: 1st: Light, Fairie Fire, Message, Secret Page. 2nd: Audible Glamour, Change Self, Invisibility, Mirror Image, Phantasmal Force. 3rd: Detect Illusions, Invisibility 10’ Radius, Phantasmal Psychedelia. 4th: Hallucinatory Terrain, Improved Invisibility, 5th: Secret Chest, Feeblemind. 6th: Phantasmal Supergoria, Veil. 7th: Mass Invisibility, Prismatic Sphere/Spray/Wall, Vanish. 8th: Symbol.
Necromancy: 1st: Invisibility to Undead, Turn Undead, Unseen Servant. 2nd: Ray of Enfeeblement. 3rd: Speak with Dead. 4th: Shadow Monsters. 5th:Animate Dead, Cloudkill, Magic Jar. 6th: Animate Dead Monsters, Shades. 7th: Simulacrum. 8th: Clone, Trap the Soul. 9th: Power Word Kill.
Prophecy: 1st: Detect Evil, Detect Magic, Identify. 2nd: Augury, Detect Invisible, Locate Object. 3rd: Clairvoyance, Detect Illusion. 4th: Detect Lie, Divination. 5th: Commune, True Seeing. 6th: Find the Path, Tongues, Legend Lore.7th: Remote Surveillance, Vision.
Animism: 1st: Bookspeak, Summoning, Unseen Servant. 2nd: Magic Mouth, Speak with Animals, Web. 3rd: Speak with Dead, Howl of the Moon, Sacrifice, Strange Waters. 4th: Speak with Plants, Growth of Plants. 5th: Insect Plague, Contact Outer Sphere, Faithful Hound. 6th: Mind Switch, Speak with Monsters. 7th: Animate Artwork, Witchlamp Aura. 8th: Maze. 9th: Imprisonment.
Speleomancy: 1st: Spider Climb, Shield. 2nd: Heat Metal, Stinking Cloud. 3rd: Water Breathing, Gaseous Form. 4th: Dig, Seven Gates. 5th: Cloudkill, Stone-shape, Wall of Stone. 6th: Find the Path, Disintegrate, Stone to Flesh. 7th: Earthquake, Reverse Gravity, Statue. 8th: Maze.