I posted that on the french Ars Magica forum and would love to have your opinions. It's a work in progress and need a lot of fine tuning.
Ideas and advice welcome
-----------------------------HISTORY-----------------------------
Forty years ago, a magus by the name Falinus Ex Bonisagus decided to explore strange and bizarre effects in the Hermetic Theory. He had spotted the fact that numerous spells vave effects tha do not comply with Bonisagus's theory, and began searching for a way to document and unify a way to use them. He met with numerous sorcerers both inside and outside the order to study those spells and effects
After years of study and research and numerous failed attempts his breakthrough is finally ready for full disclosure to the order.
He called those peculiarities excpetae and created a way to use them in spells, he descovered quite a few of them but many more must be waiting fo be found.
By 1220 his dicovery is the talk of the houses, propagating slowly in the order, the Ductus Arcanorum has just validated it and tractatus are being copied.
-----------------------------RULES-----------------------------
You just need to learn a spell, read a book or study with a teacher knowing them to use the exceptae. You can only use them with formal spells and you can't use more absolute value of exceptae than your Int+Magic Theory divided by 3. Magnitudes of exceptae add to the magnitude of the spell.
Penetrating spell (+x)
For every Magnitude of this exceptae the spell gain a +10 Penetration bonus.
You can't have a Penetration total included in a spell that exceed your Penetration score x5.
Silent spell (+2)
This spell oes not require the caster to speak
Stealthy spell (+1)
The spell can be whispered without penalty and cast silently with a -5 penalty.
Still spell (+1)
This spell does not need the caster to move.
Aimed spell (+1)
The spell is not affected by the Magic Resistance of the target but require a contested roll of Per+Finesse against Defense or Attributes + Skill of the target.
Scalable spell (+1)
Some details of the spell can be change at the moment of casting.
Multiple spell (+1)
The spell has a distinct additional effect, he use the highest base of his effects and all Arts become requisites.
Fast spell (+3)
The spell can be fast casted.
Linked spell (+2)
The spell is an Arcane connection to a specific target, beut only for casting it. You need an Arcane Connection to the target at the time of the spell invention, the spell as a Pentration multiplier as that Arcane Connection -2.
Dodgeable spell (-1)
The target can avoid the effects of the spell with an Attribute + Skill roll ease factor 9 or an Attribute or Personality Trait roll ease factor 6.
Limited spell (-1)
The spell can affact only halef the targets or lass that it should be able to affect, or works only hal of the time.
Specialised spell (-2)
The spell is designed to affect a specific individual, you need the individual or an Arcane Connection at the time of the spell invention.
Minor material spell (-1)
The spell require an easy to find and carry item that is consumed at spell casting.
Major material spell (-2)
The spell require an expensive or difficult to find or carry item that is consumed at spell casting.
Unstable spell (-1)
The spell has two more botch dice in case of botch test.
-----------------------------SPELLS -----------------------------
Curse f the werewolf Mu(Cr)/Co(An,Me) 25
This spell works only at night, it transform the target into an hideous half-man half-wolf beast increasing size by +1, strenght by +2 and decreasing quickness by -1. in addition the target grows claws and fangs (as daggers) and an unstopable crave for human flesh (has a personality trait of +6.
Base 5, Touch +1, Sun +2
Multiple spell +1x2, Limited spell -1
Stone dagger Cr/Te 20
Hurl a stone dagger to the target, she can avoid it by a Quickness + Weapon/Brawl ease 9. in case of failure damages are +20.
Base 15, +2 Voice
Dodgeable spell -1
Last resort of the flambeau Cr/Ig 25
A flickering looking ball of fire is thrown at the target, damaes are +20 with a pentration bonus of +20. In case of disaster 4 more botch dices are rolled.
Base 15, +2 Voice
Unstable spell -1x2, Penetrating spell +1x2