Another great discussion from the Ars Magica community on the official forums on Atlas games website (if you’re reading this, then go there for the full story).
A discussion of “multi-casting and the sorcerer’s fork” effects combine is a very meta-game function which is something I’d expect advanced players to have an interest in, and something that newer Ars Magica players might not know was even possible.
The essential details are that a spell from the core rulebook called The Sorcerer’s Fork (ArM p.159) allows a caster to split a single spell into two spells of lesser power. Often this is used for getting more effects from a high level spell, thereby increasing the productivity or breadth of the spell.
This allows a caster to affect two targets in a weaker manner, or more insidiously it allows the fork to be caster on a spell that another wizard is casting and thereby reducing the effect on the target.
e.g. A scenario could be that Magus Albertus is casting a nasty flame-jet spell on Magus Bartholemy. Magus A has chosen his fire spell because it inflicts a nice amount of fire damage, and he thinks his spell has a good chance of overcoming Magus B’s magical shield (aka Parma Magica).
However Magus B happens to be a master of Vim magics, and has the option of trying to cast The Sorceror’s Fork on the spell that Magus A is casting. Assuming that Magus B is able to cast cast the spell, and it works against Magus A (which we won’t worry about resolving the technical details) the nasty flame effect is split into two lower power spells, each with a reduced effect and a reduced change to break through Magus B’s magic shielding.
So if the nasty spell was a level 25 effect, with a penetration score of 30 (because Magus A is not too bad at this spell), then it becomes two level 12 effects, with a penetration score of 15 each. The level 15 penetration is much easier to reflect.
If Magus B was successful in targeting and casting The Sorceror’s Fork in this manner, he will probably be unscathed by the two greatly reduced spells.
Consider too that a beginning wizard often can cast nasty spells, but they don’t often have powerful penetration or shielding, so this trick allows a Magus to have a quasi-universal defense against hostile magic.
So it can be pretty effective. However that is not the end of the scenario which the forums were discussing.
Add to this the advantages in Ars Magica that come from “mastering” a spell, which include an option to multi-cast spells.
When a Magus chooses “multi-casting” for spell Mastery they gain the ability to cast many different instances of the same spell in the same combat round. Yes, you read that right.
In effect the spell master indicates that the caster is so familiar with the spell that they can invoke multiple versions, all with the same base power and penetration. Pretty neat, but it does take a non-trivial amount of effort to gain Mastery in a spell, and multi-casting isn’t easy.
So this is where the forum discussion started – with Magus A multi-casting an effect, and Magus B trying to defend.The question was how many spells are effected by The Sorceror’s Fork when multi-casting is involved.
In effect the defense of The Sorceror’s Fork will only work against one of the instances of the multi-cast, as the fork spell is designed to affect one spell only. The multi-caster might have one spell resisted or neutralised, but not both.
Darn cool, and dangerous too.