The way I see it is that magic is a large area that allows a lot of originality for many game developers. Unfortunately, most developers simply go for the easiest, most tried and tested methods. There have been many approaches. To my mind there are 6 distinct areas, which most developers customise to make their magic system unique. These are; the learning method, the casting method, the pyrotechnic effects (i.e. visuals), actual effects of the spell, the repercussions for the wizard of casting the spell, and finally alternative uses for the spells.
In my opinion the best magic systems are those that allow some level of customisation, i.e. allow you to create/modify spells.
Learning method:
There are several possibilities that have been used and reused. Many can be mixed and matched to allow several different methods of learning spells in one game. Here are most of the methods that come to mind:
1. The simplest method; when you level up the spell just appears inside your head. One example; Shadow hearts for the PS2.
2. The dark cloud method (i.e. Ruby the Genie?s method.). You find magical weaponry, in Ruby?s case magical rings these rings can then be customised, combined, and levelled up to make more or less powerful rings. This method sucked.
3. Find a scroll, book, or some other arcane object, memorise it or put it into a spell book. Much like D&D, many games use this method.
4. Watch the spell being performed, much like the creatures in Black and White, the more times you watch/successfully do it the easier it is to cast.
5. You pay or find an NPC to teach you the spell.
6. The final fantasy VIII approach. You draw (take) a finite number of spells from some kind of Mana well/spring, or you draw it from an enemy. When you run out of spells you either draw more of them or have none to cast.
7. The ff7 method (like the dark cloud one, only this has a lot more customisation). You find a magically imbued object like Materia (like a crystal) these Materia have their own experience system and become more powerful the more they are used. It also allows magic to be bought and sold as a commodity, with high-level Materia being highly sort after. Also Materia can be combined to allow a variety of effects (i.e. thunder-Materia mixed with all-Materia casts thunder on all enemies in a specific fight).
8. The ff10 method/not dissimilar to Diablo 2. You have a skill board of some description, you take a path on the skill board, when you activate a specific point on the board you may use that skill, and this includes spells.
9. And finally my favourite method, Morrowind. You buy a spell or find a scroll. However, you learn not only the spell but also the particular effects of the spell. These effects can then be combined, and customised, to make completely new spells. For instance if you know the shock effect and the summon effect, they can be combined to make a spell that will simultaneously shock the target and summon a demon to gnaw on him.
Casting method:
Most games use a very simple method; it is rare to see anything especially original in the casting department. Methods I have seen:
1. The morrowind / final fantasy / nwn method, select spell, click on target. That?s it, no skill involved, unless the target is moving very fast

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2. The same system, but you need to have the material components in your possession.
3. Clicking at specific times, if you click at the most opportune moments it does more damage. See shadow hearts for an example.
4. You can allow the spell to build up and it does more damage, but it takes more time, and you are vulnerable to attack, only works in real-time combat. See septerra core for an example.
5. Semantics, you type in some arcane command, which triggers the spell. i.e. what this thread is supposed to be about (me going off topic)
6. Group casting, it can be possible to have a group of mages cast a superspell
7. The black and white method. You trace a rune with the pointer and it casts the spell. This is the most innovative idea I have personally seen.
Pyrotechnics:
Well this is really more aesthetic than anything else. But good magic effects can be very cool. There is a wide scale; you can have insane amounts of slightly pretentious almost anime effects like the final fantasy games. Or you can have subtler, less impressive effects like Morrowind. And then there is middle ground like Baldur?s gate? Personally I like big explosions.
Effects of the spell:
There are thousands of possibilities. Status changes, areas of effect, damage, polymorphs, enchantments, illusions, etc? Do you limit the maximum power of a mage? Do you have mega spells such as being able to summon armies or demi-gods? Do you categorize magic into different schools (in Planeshift this is a yes)? And then on top of all these questions you have to decide how well people can defend themselves from magic.
I think there is a large scope here to come up with highly original Magic system.
Repercussions:
There have been several different methods:
1. You can only hold a finite number of spells in your mind at any given time. Every time you cast a spell you lose one of the stockpile. D&D or FF8 use a similar system.
2. You have mana/magic points, when you cast a spell these go down.
3. You lose the material components of the spell.
4. You become fatigued and need to rest.
5. You are unable to cast the spell again for a set amount of time.
6. Occasionally the spell backfires and discharges at you, or an ally.
I am sure there is more? Usually the more complicated or powerful the spell is, the more repercussions it has and the more severe they are.
Alternative uses:
For instance; in FF8 you could ?junction? your spells with weapons or armour, granting the item with magically properties. For instance if you junction a sword with a sleep spell then every time you hit with the sword there would be a percentage chance of the enemy being sent to sleep. But I believe there is plenty of scope to develop alternative uses to spells than just casting them?
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Well that?s it, that?s my analysis of computer game magic systems? Feedback? Ideas? Additions?