I want to implement a free form, role playing Magic System (like in Mage from White Wolf). Is it possible in d20? To have, the power of spells to increase, as levels go up? Any ideas about how to approach this? This is how I imagined a new version of existing magic styles:

Divine: Spontaneous, Guaranteed Effect, imaginative, High DCs, Lower Effect
Arcane Learned: Defined, Low DC, High Effect, Less Cost, Fizzle on Failure
Arcane Spontaneous: Hurtful to caster, High DC, Med. Effect, Undefined Wild Magic Results, Critical Failures

Divine: The Gods grant you a spark of their power. If they don't like you, you don't get the power. But you channel their divine, cosmic energy. So if suddenly you want a buff, you channel the gods power to buff you, or attack the enemy, or discern a location, or whatever.

Arcane Spontaneous: Pulling from the power of creation, you summon the forces of nature, titans, whoever, and you will something to occur. It is physically draining, and if you fail, it may have serious repercussions. But, if you need a web, to fly, shoot a magic missile, you just summon it. Or some combination, you propel into the sky with a mighty rocket blast, leaving a flame ball explosion (fireball and fly). The power of the spell is based upon the DC set for the attempt. (Sorcerers Archetype)

Arcane Learned: When a magic affect is studied by wizards, it is turned into a spell. So you can preform the effects of one of these spells, in a much safer, cheaper (in terms of health damage) fashion. But you are limited to an established spell. Fly, Web, etc. And, in this fashion, spell books are VERY important. In the Cthulhu lore nature. The result can also be affected by rituals, reagents, pacts, etc. (Wizards Archetype)

With Arcane, the idea is that you either study a spell, and learn how to invoke it, or you spontaneously summon the spell. Try it out. If you accomplish it enough times, and take the time to write it down, you can then turn it into a spell. And after that, it is easier for you to preform. Sorcerer's would be adept at spontaneous casting, where Wizards would be more skilled at studying the effects of the magic, creating spells, spell books, rituals, magic items & equipment.

Although I don't own it, Elements of Magic appears to be what you're looking for.

I have tried a few times to run with freeform magic systems and i don´t think that the "learned part" is going to work. The reason for this is that finding the line when a spell is different from another spell is difficult and will put stuff into boxes (which i find ruins the whole point of having a freeform magic system). 
There is also the question of how much more difficult freeform spells are, and if they have a fixed failure they might never be used (Tharlos the all seeing eye fail to cast a light spell 3 times in a row because he didn´t pratice it, would properly discourage him from ever using none learned spells again).

I found out the easiest way to "control" the spell access was to make categories of spells (fire spells, force spells, wind spells, negative energy spells etc...) and then create levels within these (a mage of first circle within force spells can only keep static forces like a force armor where a third circle can use telekinesis). This of course also depends on your campaign if your players want to go on chases for spells this might not be the best way.

What about having the DM set a DC on the spot for each spell as described by the player, and then the caster has a certain base value for the magic of their "circle/school", and maybe a secondary base value for spells tangent to or outside their "circle/school."  As the magic user gains levels their base values grow.  Of course, rolling a 1 on the D20 when casting the spell would mute its effects.  As far as spells per day, maybe you could come up with a certain number that represents the total DCs in spells the caster can use each day (they then subtract out the DCs of the spells they attempt).  I don't -for "ethical reasons" I don't own much D20 stuff and I'm a little tired, let me know if this makes sense and/or sounds good.

Louis Hoefer
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Have you looked at Monte Cook's World of Darkness RPG? If I remember correctly, it has a system for spontaneous creation of spells by using a few "effects" charts. It also has some sample spells statted out according to those charts for characters who want a pre-determined list to work from.

And it's a d20 product! :-)

That's beautiful. Thanks!

Finarvyn wrote:
Have you looked at Monte Cook's World of Darkness RPG? If I remember correctly, it has a system for spontaneous creation of spells by using a few "effects" charts. It also has some sample spells statted out according to those charts for characters who want a pre-determined list to work from.

And it's a d20 product! :-)

This reminds me of a gigantic project I worked on at Giant in the Playgrounds to create a "bending" system based on Nickelodeon's Avatar: the Last Airbender.
You may find this interesting.
links to the main site and forum hq for the creation of the system.  You could change "seeds known" to spell lists, and have different DC's depending on the type of caster, and modify the overbending mechanic to fit the classes depending on your hurt with failure or fizzling rules.