I and my troupe have some problems with multiple casting.
The thing is that some of our magi have a mastery 2 with fast casting (or penetration or other thing) and Multiple casting.
If i correctly read the rules, that means he can cast 2 copies and 1 original, then 3 spells in one rounds; with 3 casting dies and so 3 casting totals.
For each casting total : * A botche means the 3 spells botches
A fail by less than 10 mean a fatigue level lost, like for a "normal" casting.
A success, the spell is cast.
But, where we are quite disappointed it's with the "easy" side of multiple casting.
On my internet downloaded character sheet, i read that there would exist some "multiple casting die", which is int+finesse -number of spells (copies or all, copies + original?) VS an ease factor of 9, needed to check if the magus CAN , or not, multiple cast this round.
But, i can't find this formula in the core book...
It's not easy at all! It takes a lot of experience points to get your Mastery score up to a point where you are flinging off many multiple copies. it takes 105 xps to get a Mastery score of 6 (or only 50 if you have the Flawless Magic Virtue), which allows for a maximum of 7 spells. The old formula, requiring a roll, allowed that many as possible with a mastery of only 1.
It takes only 3 seasons (15 xp) to get mastery 2 and cast 3 copies (original and 2 copies). If you are going at a single target, it is only a -1 casting (with +2 for the mastery) to hit same person with all three spells. This can be very devistating.
It is very easy. In 3rd and 4th edition, you had int+finesse - number of copies vs TN 9 to get off the casting. This made it somewhat harder to do many spells.
I am not sure how to offset how easy it is other than perhaps -1 per copy cast period.
Yeah, but under the old-old rule (xp = to magnitude to master); if you had Int +3 & Finesse +3, you only need to roll a 5 or better to cast the three spells. Very achievable, especially if you are willing to spend Confidence. It took a 9 or better to get seven spells, which is not so easy but still within the realm of possibility, and it took only a single season of mastery to be able to do this. The current multi-casting rule works just fine in my opinion.
Check the eratta. You get the original and copies equal to your mastery score. And you can Fast Cast and Multi Cast at the same time. The bit about not exploiting other casting options is in reference to Words & Gestures.
Whether you can multi-cast while fast-casting is not answered by the eratta. (serf's Parma) The RAW states that you cannot use words&gestures or other casting options. (/serf's Parma) It has been argued on this forum that multi-casting is such a casting option and can therefore not be used.
Back on the power of multiple casting:
It takes some time to master spells (3 seasons is a lot I think).
You can only do this with formulaic spells.
It's not usefull for a lot of spells.
Therefore it should give you serious power.
Do remember that one big hitter does more damage than a couple of smaller spells. So focussing on a really strong fireball is often better than group or multi cast ones. (xp wise)
(1 incapacitating hit is better than 3 heavy wounds IMO)
I would rather multicast 3 level 5 or level 10 spells with +20 penetration than one level 20 spell with +10 penetration.
I created a demon hunter flambeau with mastery 3 (multicast, penetration, stalwart casting) for DEO 10.
As she is Apromor mage with pussiant, I think her casting total is stress+25+aura, her penetration is (casting stress die) + 22+aura. If she wounds the demon with her sword to get some blood, penetration is suddenly (casting stress die) + 36+aura. Against an infernal might 20 foe, she automatically casts two and drains it of 20 might (gone). AGainst infernal might 30 foe, she has a good chance to penetrate with 2-3 of them per round (in a strong magic aura, 3-4). If she wounds it, she has good chance to take down an infernal might 40 in 1 round.
If she had a DEO 20, her penetration would have been 12+aura+casting stress (or 26). meaning work to penetrate Infernal might 20 and unlikely to penetrate infernal might 30 (without arcane connection). DEO 30, she would be lucky to get the spell off with no hope of penetrating.
Lower level spells multi-cast is a lot more effective than high level spell when facing foes with magic resistance. Note, this is a maga just past her gauntlet. (flawless magic, mastered spells virtues)
Yes, against higher magic resistance foes, this is true, as several have been saying, too.
But that doesn't mean those on the other side are incorrect. I think it depends on your typical opponents. What would you rather use on the non-magical elephant about to trample you? Your multi-cast level 10 PeAn thing probably won't affect it (too large for Individual). It probably won't notice your multi-cast Crystal Dart. But that BoAF is going to do something. Of course, multi-casting BoAF would be even better.