Back when I played 2nd Edition AD&D, I thought the magic system was flawed. It was entirely arbitrary and unbalanced, at least in my opinion. I wanted something more fair, but all my attempts to build something better just didn't work out.

Then I started playing GURPS and found out (after making one mage) just how flawed it's magic system is. It's balanced, but it just takes far too long to build a mage and one fire mage is almost exactly like any other, spell-wise, due to prerequisites. This was back in the days of Third Edition.

Here's my big complaint with the standard magic system: Unlike most of GURPS, it simply isn't generic or universal and thus, I refuse to use it. I cannot emulate Dungeons and Dragons magic with it, because it's just too different. I cannot emulate any other RPG's magic system with it. Period. It's just fixed and inflexible and making new spells is ridiculous guess work, just like with AD&D.

Then I heard about 4th Edition and eagerly awaited it, hoping they'd fix the magic system and actually make it universal. No such luck, but they did fix the psionics system. When I saw what they did there I thought it was awesome and wished they'd done the same thing with magic. Instead they're still treating it as a special case, the last one built into the system, I might add.

It was shortly after this point that I realized 4th edition is flexible enough to build literally anything on a character sheet. Including a rock. Or a car. Or…you get the picture. When you add in the Powers book, things get even easier. Between the two books and some creativity with modifiers, they cover everything.

So I had the idea: why not build spells the same way?

That was the inspiration for my magic system: the Generic Universal Magic System (GUMS). For the basis of my system, I began with a desire to emulate AD&D, but make it actually easy and balanced to build new spells. At the same time I wanted to make it easy to modify to emulate almost any system out there.

For starters, you've got to have an Advantage that spell-casting characters take. The old Magery advantage just didn't fit my needs, so I started from scratch with Modular Abilities, on p. B71. Eventually, after much work, I ended up with something that looks like this, working from the way magic works in AD&D:

Modular Abilities (Super-Memorization) 
    Spells Only, -20% 
    Takes Extra Time 1, -10% 
    Switching Spells Requires Preparation (1 hour), -50% 
    Keeping them prepared requires daily preparation, -15% 
    Limited Use (spells become unprepared after use), -40% 
    Affects Substantial (at -3), +40% 
    Affects Insubstantial (at -3), +20% 

This covers the very most basic, standard assumptions of how magic works in AD&D. Spells become unprepared after use, requiring study and meditation time to prepare them again. I'll call this preparing spells instead of memorizing them. The word memorize as used in AD&D always bugged me. It just sounds stupid, in my opinion. People just don't forget stuff so easily. For lack of a better name I'll call this Standard Magery.

After all the math, this costs 1.25 points + 0.75 points/level and each level allows a character to prepare one point of spells.

Now, with this basic bit of work, you can change modifiers and make new versions of magery, given different assumptions about how it should work. For example, say you want to cast spells using fatigue, similar to a standard GURPS mage:

Modular Abilities (Super-Memorization) 
    Spells Only, -20% 
    Takes Extra Time 1, -10% 
    Switching Spells Requires Preparation (1 hour), -50% 
    Keeping them prepared requires daily preparation, -15% 
    Costs Fatigue (1 FP/10 points of spell, round to nearest FP) (-40%) 
    Affects Substantial (at -3), +40% 
    Affects Insubstantial (at -3), +20% 

Now, it took some juggling with the fatigue cost, but I think the result is fair and this is far less arbitrary than other systems I've dealt with. The arbitrary part is limited to modifiers on magery, instead of every stinking spell you build. I call this one Fatigue Magery. It costs the same as Standard Magery.

Note: Mages can will their spells to end at any time unless you limit this out or the spell description says different.

Of course, players are going to refuse to put all of that on a character sheet. It's just too much, so we simplify it and just call the whole shabam a new advantage, rounding up the cost to whole numbers (2 points + 1/level). You can always look back here if you've forgotten exactly how the advantage works. Any time you make a new version of Magery, go ahead and write down how you made it and show it to your players so they can see how it works.

The beauty of this is that spells are easy to make. You just build them as a collection of Advantages with modifiers and don't bother with the flowery description unless a little bit of explanation is required. The real beauty is that they're automatically balanced, because they're built with points!

They also provide the flavor of the magic system. Each magic system you want to emulate will likely require all spells to be built a specific way, with certain components being mandatory.

For example, you're free to insist that all spells require Spell Components of some kind to activate. This could be a gesture, materials, full on dancing, etc. Use the commonality options from Trigger on p. 115. This is how I treat it: hand gestures, facial expressions or words are very common and foot movements are common. If you're using materials, too, start with the rarity of the materials and modify by the rarity of the other parts of the trigger. Regardless of how many components you throw in, it never becomes more complex than rare. If the materials cannot be reused for another casting of the spell, consider raising the rarity another notch to compensate for the added irritation of obtaining them all over again.

For example, a spell requiring dirt (very common) and hand gestures (very common), become common together. If it also required words, it would become occasional. If it were sand (common) instead of dirt, it would bump it all the way up to rare.

Due to the nature of Limited Use and Costs Fatigue, the natural duration of any spell is 1 use or 1 minute, depending on the particular advantages involved. This can be modified by adding Extended Duration. I suggest always having a limitation built into Magery that keeps this duration. With Costs Fatigue, spells may be maintained by paying half the fatigue cost again. Isn't that neat?

One level of Reduced Time on a spell makes it a free action and possibly allows it to be used as an active defense.

To emulate spell-casting of most magic systems I've seen, I suggest requiring Spell Components with at least one non-material component and requiring a limitation built into Magery that forces the 1 minute duration mentioned above.

I also suggest that most spells should be enhanced with Malediction at the +100% level, as this exactly mimics the way a Regular spell works. I would also say it's a fair enhancement to add Based on Activation Roll for +20%, which means that the original activation roll (see the next section) is the caster's half of the contest of skill. However, the target's half is still based on Will.

Note: All spells must have the -10% Magical power modifier from GURPS Powers. Magery itself isn't magical, but the spells are. This is just my personal preference, but others may choose to do things differently.

Hrm, we did leave that out. For this one, you've got to go back and modify your Magery advantage(s), because without this, there's no difficulty in activating spells; they always work unless the caster is interrupted (the AD&D way) or they require a second roll to actually succeed.

To make this work, I'm taking the Requires (Attribute) Roll limitation from Powers, p. 112 and changing it slightly, since this is similar. We'll call it Requires (Skill) Roll, worth -5% and change things as below:

Modular Abilities (Super-Memorization) 
    Spells Only, -20% 
    Requires Skill Roll, -5% 
    Takes Extra Time 1, -10% 
    Switching Spells Requires Preparation (1 hour), -50% 
    Keeping them prepared requires daily preparation, -15% 
    Limited Use (spells become unprepared after use), -40% 
    Affects Substantial (at -3), +40% 
    Affects Insubstantial (at -3), +20% 

This drops the cost down to 1 + .6/level and it hits the modifier limit of -80%. Fatigue Magery is so close that it will have this cost as well.

Now this brings up the question, what skill do we roll against? This again gives you another option to emulate other magic systems. You could use rune skills, a skill specific to each spell (if you wanna emulate the standard GURPS system), or you could do as I usually choose and make a new skills for each individual college of magic. These colleges are somewhat borrowed from AD&D and by description, you can determine what college each spell falls under. You can even have minor colleges that cover smaller areas and are easier to learn.

The base colleges will be IQ/Hard skills that default to Thaumatology-6 (borrowing a little from the ritual magic system on p. M200). Minor colleges may be easier than this, based on how broad their scope is. Individual spells may be improved as though they were Hard techniques. No individual college's skill may exceed Thaumatology skill.

In writing spell descriptions for this system, I determine each spell's base college(s) and put it into the description to ease later use. Minor colleges for the spell can be determined fairly easily during game play based on description.

This requires that mages make skill rolls for their spells, but it has the usual effect. Those using Standard Magery who get a critical success don't have the spell go unprepared after use.

This may require some reworking depending on what you want to do. It works fairly normally for Fatigue Magery. Personally, I ignore the bits about people without magery being able to cast spells. I always thought that was weird anyway.

For Standard Magery, the mage's spells don't become unprepared when cast in a Very High Mana area.

For the magic system I'm using with Islands of War, I'm using a few different Magery versions that are all very much the same with the above activation rolls, based on skills for the individual colleges of magic and a default 1 minute duration.

You can find out more on the Advantages and Skills pages.

Good question.

There's a couple of ways to handle this. Both are covered on Powers, p. 40.

Unquestioningly beneficial afflictions have a duration in minutes equal to the margin of success for the HT roll.

The other alternative is to build all beneficial afflictions using the Malediction enhancement (p. B106). This allows the target to waive their resistance roll and the duration becomes the margin of success for the caster's Will roll.

This is easy. Build a spell based on Modular Abilities (Cosmic Power). Add a Trigger limitation (if you require these) for reciting a poem or something of the sort. You're free to add other limitations, such as Fickle (p. POW110), to represent the GM's tendency to interpret the results according to the poem's wording. I would interpret this reaction roll as a normal one, however, instead of a simple pass/fail test. The better the reaction, the better the spell works. The worse the reaction, the more twisted the result.

As to which skill to roll against for activation, the spell should use whichever college is most appropriate to the desired effect (if using my college system).

This is just one example, however. Build your own version. Have fun with it.