Once again, nothing groundbreaking with the basic mechanic. PCs have a skill that allows them to use magic:

Wizardry (for casting arcane spells)
Ritual (for casting divine spells)
Rune (for creating magically items)
Alchemy (lotions and potions)

Spells have a difficulty rating based on the various components of the spell (what it does, how many targets/size of the affected area, range, duration, etc.). A spell might look like this:

Fireball
Diff: 19
Range: Close
Area: Table
Duration: Instant
Drain: 9 pts / die

This spell creates a ball of fire which explodes affecting all within its area, causing D4 per dice of damage to all character within the area--friendly or not.

To cast a spell a character combines his Skill + Attribute Bonus + modifiers + D20 vs. the spell's Diff (Difficulty Rating). If he rolls higher than the difficulty rating, he successfully casts the spells. If not, he either has to continue casting the spell or there is a chance of a miscast--and dire consequences.

If the spell caster can cast the spell with a Take 5 (Heroic Roll of 5), then no roll is neccessary, he automatically casts the spell.

Casting components and other objects can be used as casting modifiers. Such as a wand made of burn wood to cast any fire-related spell could be worth +1 or +2 bonus.

Furthermore, a player can alter 1 component of the spell when his character is casting it--which in turn could affect the spells difficulty or total drain. For example, you want to cause D6 per die instead of D4, the difficulty just shot up to 23 and a drain of 13.

Drain indicates how much Spirit is drained when a spell is cast. Every character has a Life (HP) score and a Spirit score. Spirit is a measurement of how much magic they can manipulate. For example, if a character wanted to use the spell above to do a 4D4 fireball, it would drain 36 Spirit points.

If your character had a Spirit of 108, he could cast this spell 3 times, which would completely drain his spirit.

Character's can augment their Spirit by using casting component-which are consumed and reduce the total drain or other artifacts that suppliment each spell cast by a number of points. There are all kinds of opportunities for boosting/supplementing a character's Spirit.

Lastly, A character can memorize 1 spell for each attribute point of Intelligence and Wisdom. These spells are not forgotten when used. A character with a Spirit of 100 who memorized a Magic Missile spell that only drains 4 pts per missile could either cast a single spell doing 25D4 or cast the same spell 25 times.

Spells using massive amounts of Spirit are more difficult to cast, I should note.

Additional spells can be read from scrolls, speel books, spell staffs, spell wands, etc. For example, a 1st character could inherit a book of spells from a family member with over 100 spells in it. He could use them all--however, the more difficult ones would likely end in him killing himself.

EXAMPLE

A 1s Level wizard casting the fireball spell would determine his total modifier first. He could potentially have a Wizardry skill of 3, Intelligence modifier of +3, and a burnt piece of wood +1 (-1 drain). His total casting modifier would be +7 with a -1 to the spells total drain.

He rolls a D20 adding it to his modifier.

If he rolls a total of 9 or less, the spell fumbles and he has to roll on the spell casting fumble table--never a good thing.

If he rolls a total  10-19, he simply must continue casting the spell. If he is interrupted--by being attacked, affected by another spell, etc.--then he loses his concentration and the spell fails, draining a minimal amount of spirit.

If he rolls a total of 20-29 he successfully casts the spell, whcih drains 9pts per die. If he chooses 3D4, it would drain a total of 24 points (9 - 1 for the component). Or he could simply choose to do 1D4 fireball over three turns--once cast, a character does not have to recast a spell to use it again as long as he is not interrupted.

If he rolls a total of 30+ he successfully casts the spell and can choose to upgrade the spell's effects by 1 level or reduce the drain by half. If he upgraded, he could do 1D6 for the cost of a 1D4, or his D4 die would cost 4pts each--3 pts after the component.

Rune and Alchemy powers basically allow a character to store a spell in an object and release it later. A character can create as many objects as possible using his Spirit or another character's Spirit. Once the spell is used, the Spirit is released and the character from which it came can recover it.

That's it in a nutshell. Any comments?

Are there other systems that require a magic die roll?

In the latest rules discussion, mini play we are looking at a spell cast roll to cast/hit an opponent. For example, if the character were going to cast a simple Mystic Missile spell wiht a diff of 14 at a character with an Armor score of 16, he would use the Armor score of 16 for the task resolution, not the 14. So basically, whichever is higher, the spell's Difficulty or the Armor, Dodge, Block or Will defense.

This creates situations where a noble adventurer with a huge +3 magic shield could block a fire ball with a Block defense of 23 versus the evil wizards spell roll of 21.

Just some ideas we are tossing around.

I can think of D&D 4e (although those are not very freeform), Shadowrun 4e, Iron Heroes, Rustbelt's alternate magic rules, and one or more of Burning Wheel's magic systems. Almost all systems that use unified mechanics apply those to magic also (it's part of the ideal of a unified mechanic!), and my one will too eventually hopefully. My system uses prepared spells with pre-set powers rolled at the time of prep, which I thought could be pretty cute, as you will one day have a very strong fireball, and another day one the size of a tennis ball. But the fact you know the power before casting replicates some of the "6th level fireball" feeling and to an extent makes them more reliable.

But on your system, there is so much opportunity for creating interesting overlaps; the component "trade" can join the mages to the populace, so those that do not alienate people will be able to get components easier, and so be more powerful, etc. I notice that in your current system a harder spell is harder to avoid. I can see the attraction in that, in my system it is generally the opposite way round, which is based on a previously considered choice, less suited to your more spur of the moment system. I can see the drama in your version, so if someone is casting for ages, you know it's probably going to turn out nails! Actually I got that wrong, I thought that you rolled the skill check and compared to defence, and so you could gain the power to cast, but not enough to penetrate their defences. In that case you could actually have it that you can continue to cast in the hope of adding to your roll, say a +5 to effective power level for each successful cast (20+). This replicates how D&D magic users would sometimes behave when faced by a high magic-resistance person; they would cast intermediary spells to boost the power (effective caster level, but you get the idea). I've been trying to work out a more elegant system for that idea, it seems like you could have a system where people slowly crank up the power, but with the potential perhaps that at every stage the drain on failure increases by the same amount as the bonus, so summoning up all that power can be very risky for an inexperienced mage.

One possibility for the mechanic could be three numbers, the failure value, which is unaltered, and the success and critical threshold, which take bonuses from components or casting rounds. This would stop people using components so that they cannot fail. I quite like the idea that people can start trying to cast this complex spell while others try to shelter them from missile fire and other interceptors.

What happens is spirit drain goes above remaining spirit? The classic solution is damage, but I might make it more hardcore than that, certainly including collapse, so it's a really hard limit.

Once you've got the system as you like it I'd suggest you grab as many spell effect types as you can and then get the spell casting/combat/social arrangement interacting in a fun way, and then test the system to infinity! If you can make playtesting fun enough, then you can build up enough intuition to be able to start eyeballing the power level of spells, perhaps creating some kind of template.

Arguably the best classical magic system is found in Ars Magica...

(I say arguably because I've heard a lot of people say that it's "hands-down the best". When I've heard people say that other systems are better there are few who can agree on which of these other systems is superior).

You might want to have a look at that.

V