Magic has to have a power source. Power (for game purposes) comes in units. Spells take some number of units to power.
System - In general a spell takes 1 unit per 10, so a 1W spell takes 2 units, and so on. This may be effected by the efficiency of the magic, which changes the effect given per unit.
The power sources are few. You can source off your own inner energy, through focused meditation - this is the traditional wizard's route. You can get around ten units per day this way, when you're good.
System - a sorcerer has the skill meditate, and tests it vs 10 + the total number of points they already have. Success gets one point, marginal success takes half an hour, normal 10 minutes, and total is either 5 minutes or two points. A marginal failure means try again immediately, normal failure means that another attempt is impossible today, and a total failure will result in the loss of some power.
You can source off someone else, through blood. A typical human (or half-elf) has 20 units worth of blood (that's about one unit per cup, for those of you keeping score), but bleeding 2 (a pint) makes a person tired, and bleeding more than 5 puts them down for a while. Full elves have about twice as much blood energy, but regenerate it more slowly. Animal blood is weaker in potency, but they may have more - cows are big. A rule of thumb is that animals are a tenth as potent as humans, although bugs or fish are probably so much worse that sacrificing them would be pointless. Blood is the favorite source of the elves, who have special blood creatures to create more potent blood - including the blood tree. Blood can be stored in specially prepared containers. The elves have living blood gourd plants that can do this, or a sorcerer could enchant one, or one could be created through glyph magic. For the purpose of the game, humans regenerate a single point of blood with a good night's sleep and a hearty meal.
System - well, actually, this is trivial, although some sort of surgery test is required to bleed more than a point without bleeding too much.
The last power source is the gods, which have nearly bottomless sources of power (though not actually bottomless). They give it to worshipers who honor the old compacts by praying. A devout person might be able to get a unit every now and then. A totally devoted high priest might get 100 in a year, often in a giant lump or two to do something miraculous. Divine magic may not be stored within a person, though it can be stored within a holy item.
System - a person may use their Worship God skill in order to pray for a favor (a single unit) at difficulty 17, +20 per favor received in the past year or so. Obviously not likely! A real go getter may pray for a miracle at difficulty 10W6 or 10W9 depending on how big the god is, and will get a specific effect or a large number of points.
Magic which has a natural duration doesn't take the duration modifiers in the basic Heroquest rules - for example, magic that enables a trip lasts all trip. Also, magic is not physics. Making something large move is not greatly harder than moving something small, and logically you can derive more energy from it if you were to hook that moving thing to something else. The targeting modifiers from Heroquest are a decent guide.
Sorcerous Ritual Magic is 200% efficient and uses your own energy, but requires exotic components and a long time. Basically you're gathering extra units from the ether (really it's only 100% efficient, but you are taking in energy the whole time). Each family of rituals must be learned separately, or created through extensive research. Sorcerous rituals may make permanent enchantments. A quick guideline for how long a ritual takes is 1 hour per 10 of the effect level - or 2 hours per unit expended.
Sorcerous Magic is 100% efficient and uses your own energy, requiring magic incantations and gestures. This is the form of magic to measure other things from. Each spell must be learned separately after the family of rituals is already known.
Sorcerous magic is used by humans, elves, and half-elves, though it is not common amoung any of those races.
System - learning a tome of rituals is like learning a grimoire, and learning a spell is like learning a spell out of a grimoire. Research rolls may be required to understand the code or language that the grimoire is written in, but there are no checks like the talisman construction checks from Heroquest.
Divine Miracles are 100% efficient using divine magic stored within a person. These are not much practiced any more. Divine miracles may make permanent enchantments. As far as anyone knows only humans have ever had access to divine miracles.
System - Divine Miracles are generally improvised off the users Worship God skill at at least a -5 penalty. It used to be possible to learn more specific miracle skills to reduce improvisational penalties, but those talents are basically lost. The presence of a prayer mill worshipping the god in question in the area will impose further negative modifiers, as will the global proliferation of such mills.
Glyph Magic is only 25-50% efficient, and uses divine magic stored within an object, focused through another object. Glyph magic can only make magical items, although those could of course be as simple as the paper the glyph is recorded on plus an attached divine power token.
Glyph magic cannot do anything permanent, though with a continual power source it can keep operating forever. Glyphs that run out of power can be reused by providing more power, they're essentially permanent magic. Glyphs are made with a given strength that never changes. The efficiency of glyphs is climbing - the best modern glyphs are 50% efficient, while older glyphs may be 33% or 25% efficient, or even 10% for glyphs drawn before the modern era.
There is a glyph to convert blood into power for another glyph, which was their main mode of use before the divine magic breakthrough. This costs 1 unit per unit transferred, and with 50% efficiency that cost is multiplied by 2, so the overall efficiency of the transfer is 33%. Of course, the other glyph also operates at 50% efficiency. There is also a glyph to charge an item (for transferring energy from one store to another) which again costs 1 per 1 unit moved with a 50% hit making the total efficiency 33%. Round down.
Glyphs may be made by copying an existing design, which is a fairly simple task, or by creating a new design using the principles of glyphs, best left to experts. Glyphs are written down in huge tomes and guarded jealously by the manufacturers. The important thing about copying a glyph is that not only does the physical pattern need to be correct, the mental pattern while inscribing it must also be correct. The physical pattern is easily copied from an existing glyph, but it is impossible to tell what must be held in the mind while making it. Glyph tomes will of course record this as well.
The object that the glyph is attached to is also important, and generally must be of high quality (though not ridiculously so - one can glyph enchant a quality sword, it needn't be meteoric iron). The glyph must be varied depending on the object it is attached to, so a glyph engraved on a bronze wand to make it a fire wand will be slightly different from one on a steel wand.
Glyph magic is culturally human - as far as anyone knows, only humans have the gods, or the correct type of gods, to power glyph magic. Others may however use glyph magic artifacts purchased from humans.
Glyph arcanology is revolutionizing human societies almost everywhere by allowing many things that could not be done to be done (such as the questioning helmet) and in allowing earlier processes to be more efficient. One thing glyphs are not used for much is labor-saving devices and appliances. Anyone who can afford to buy glyphs can afford to hire servants, who are more flexible and don't get stolen.
System - glyphs are purchased like spirit charms, and have a rated effect. Glyphs are part of a particular piece of equipment, such as a fire crossbow which has the glyph Flaming Bolt 5W. It uses 6 units per shot and adds a +3 enhancement bonus to your attack (added to the bonus you already get from a crossbow). Designing a new glyph is a test against the rating of the glyph desired - for example, to create a "Fly 10W" glyph the creator tests glyph skill against 10W. Failures result in a glyph of reduced power and/or efficiency. High success will allow a more efficient glyph (up to 50%) that hits or exceeds the power level. Copying a glyph from a diagram book halves the difficulty of the test, so making a copy of "Fly 10W" only tests against a 15. It is not possible to make a better or more efficient glyph by copying, however.
Blood Magic is 200% efficient, using blood magic to make changes in an organism, with no other possible effects. Blood magic can make permanent changes in a being by using a great deal of extra power. Blood magic is performed by blood rituals, which are formed into families or ways, and take quite some time. There is also a quick form of blood magic that can be used like sorcerous spells, but it is only 25% efficient. Blood tends to go everywhere during that sort of thing, and even the quick form cannot do anything other than make changes in an organism.
The final and least common form of blood magic is alchemy and potion magic, which is only 100% efficient but may be made into potions which can be used at a later date. Alchemical magic can also transform non-living things. Alchemy is probably the least common form of magic, excepting divine magic. Blood magic is culturally elvish, with very few humans using it. Humans who do use blood magic almost universally use alchemy, and its use is growing more quickly than any other excepting glyph magic.
System - Learning a way is like learning a grimoire, and learning separate blood spells is like learning a spell. Alchemy can only be learned as spells (potions). Most elves don't bother to learn spells or use alchemy. Creatures can be enchanted to be something like living glyphs by using the proper ways and increasing the duration, and can be purchased by a character in the same manner as glyph devices. Increasing the duration beyond permanent can make changes which will be inherited by the creatures children.
Tattoo Magic is 100% efficient, using the blood energy of the person with the tattoo (and no other). It's sort of a combination of glyph magic and blood magic, and is very lower class. Once you have a tattoo it can be reused forever - or at least until you run out of blood. Tattoos are made with a given strength that never changes.
System - Tattoos are bought like spirit charms, and can be used actively if appropriate. Each tattoo has a single ability and can never be changed. Activating them doesn't take a separate action, although if they use a lot of power stopping your own bleeding might. In general tattoos are not available over 14W in power - that uses three units of blood, which is as much as most people care to lose even in desperate situations. There are a few exceptions of course.
There's a special tattoo that can be used in order to convert divine power stored in an object to internal power, the sorcerer's tattoo, always placed on a hand and powered by one unit of blood energy. The conversion is inefficient, running at half the sorcerer's meditation skill, but even so this is much used by sorcerers in modern times. Getting magic in this way damages the sorcerer's meditation ability.