Ok, this is meant to simulate an unstable magic power even for experienced characters. System uses 2d6 and adds a modifier which varies from 1-4 depending on the "soul" stat of the character. Since characters learn from different kind of magic schools along the game, magic rules can be quite different from one school to another. Say, for Elemental magic, the character first needs to do a pact with an elemental to gain access to it's powers. Then he can roll 2d6+soul which indicates the amount of damage in hit points and the area covered in cubic meters.

So let's say Pedro has a pact with a Salamander, he gains access to low level fire magic and wants to fry a few zombies. He rolls a 9 on the dice, adds 3 from his soul stat to get a total of 12. That's 12 adyacent cubic meters of fire, disposed in any way he wants, be either towered, in line, as a wall, etc as long as they are adyacent. Target catching flames is only possible on a natural roll of 12, bu then the total damage is applied each turn unless fire is put off.

For high levels of magic the result of 2d6+soul is multiplied by 2, 3, etc. according to the power of the creature the mage made the pact with. Since all characters in the game are mages, and battles doesn't last for too long spells casted per day have no limit.

¿Looks too complex? ¿have you ever heard of another similar mechanic? ¿Does anybody have any helpful questions/ideas for other schools of magic?
I'm still working on necromancy, alchemy, summoning, healing (which will include buff magics), and illusion, all work differently.

I'm also wondering if this system and the way it's revealed to players may work to make magic look like something mysterious instead of something that has no secrets to players. There's also the issue of the botched spell - would it ruin the fun to add a rule where on a natural roll of 2 magic gets out of control? have you ever hated a magic system for how often this happened to your character?

WM,
 Well, the mechanics seem decent. I wonder if non-spell casters see this same sort of exponential power growth for high rolls? It might be important to balance this against melee attacks (unless you want to encourage most players to be casters of some kind).

  As to mystery, well, I am not sure how that would work. I mean, it sounds like there is a lot to invest in magic and then not know how it works. You need skill points, stat points, knowledge of something to make a pact with and then successfully make that pact. Seems like an awful lot to go through and not know what you get in return. And, the magic is already unreliable. You can only predict the range of your spells as a chance that you can roll so high...

  I guess one way you could make it work is to secretly determine what kind of entity the character must make a pact with. Like maybe their mentor tells them, "Quest to  the cave of Caer Crag and find your power there" And then have the character discover what is there and later agree to do any one thing in exchange for access to its magic power. In this way, the players know they are getting something cool, but they don't know what, until they go find out. And then there is another mystery surrounding THAT discovery.

  As to the Botch, I think it could go either way. I mean if a Botch meant you lit yourself on fire, well that bogus and dumb. If a Botch meant that the Salamander took something you said the wrong way and you had to have a conversation with it after the fight, then that is amazing! I guess the answer shold be , if it happened to you while you were playing, would you be cool with it, right?

  But, you are definitely on a good starting path, keep it up man!

Gee, thanks a lot Dindenver!

Yep, you were right, all players are casters of some kind, and of what kind depends on the choices they make on the story. Pacts are made as a quest, mentors give you an idea of where you can make the pact and how, the rest is up to you and the creature you make the pact with. Perhaps I should make a table to have the creature ask for something random in return for it's power. So it's like roleplaying the days when your character was just begining to learn magic, every day something amazing appears in your life and you get a chance to get a hold of it, depending on your decisions and luck.

So I stll can keep character sheet clean except for 3 characteristics and hit points. It isn't exactly a rule lite system, but one with a slow learning curve. I like the idea that they aren't tell fully what they get from the pact, perhaps the creature gives them a mark or item that can be interpreted by an experienced mage. I like your idea about the botch, it's already a bad thing that your magic doesn't work properly in battle, but a botch while making the pact is possible if you don't ask things properly. Many thanks!

It's really hard to make magic seem mysterious. Really, the more rules you dedicate to the magic, the less mysterious it can become. Well, that's not entirely true. If you create a single, elegant, unified system for magic, it's likely to feel scientific and predictable. If you create a bunch of different spells or effects, each with their own rules (a la D&D prior to 4E), it can feel pretty unpredictable.

Another way to make magic mysterious or unpredictable is to have some kind of "agent" deliver the spells. If you have to make deals with spirits or angels to bring about your magic, and each time, these agents want stuff from you, casting can be different every time. Be careful you don't put your players (who imagine their wizards as potent forces) into a "mother, may I?" situation.