Fast Casting in response to your own actions

We had this kind of situation pop up in our last session:

On her initiative of 7, a maga casts a spell, opening up a deep pit beneath her target (who would go on 5).

As her target falls, she decides to fast cast another spell on the target.

So...

Can the maga fast cast in response to her own spell?
Would she need to beat her own 7 on the casting speed roll or the target's 5?
If there's nothing in the rules to prevent this kind of action, would you allow/prevent it and why?

You can't cast a normal spell and a fast cast spell in the same round. I don't have my book with me to give you a page number, the text is in the combat chapter. We had a discussion a few weeks back regarding how it is worded unclearly.

I'll look out for that other thread again, but the wording on page 174 seems to suggest that a magus can manage a regular casting AND a fast cast spell in a round.

The wording is a little vague and I'd tend to apply the stated mechanics to the scenario; you can cast a normal spell and react with fast cast spells until you can't make the quickness roll.

I guess that's my problem with the scenario I stated. I couldn't see anything (beyond this paragraph) that prevented the maga from doing it, but it felt so wrong...

The page 173 quote is the one I was referring to

The sentence

"Thus, a magus can not cast more than one normal
spell, or a fast cast and a normal spell in the same
round."

should be read as:

Thus, a magus can not cast:
A) more than one normal spell,
or
B) a fast cast and a normal spell in the same round.

Here's the link to the previous discussion

https://forum.atlas-games.com/t/really-quick-fast-casting-questions-like-lightning/1721/40

Ew.

So, in magical combat, assuming roughly equal magi, where I imagined:

magus A casts spell, magus B counters
magus B casts spell, magus A counters

back and forth until someone wins, this interpretation of the rules - which I guess is official - leads to:

magus A casts spell, magus B counters
magus B can't cast a spell because he just countered
magus A casts spell, magus B counters
magus B again can't cast a spell...
magus A casts spell...
etc.

until magus B gets tired and passes out, or fails to counter.

Edit: Wait a second... what about the rules for casting multiple fast cast spells in one round; middle column of page 83 of the core book, in the paragraph right after the 'fast casting speed' calculation. Has that been errata'd out?

Edit x2: Ah, I see. Multiple fast-casts are allowed by the next sentence after the part you're quoting. That answers my Edit: question, but not the original problem.

Thanks for the link. In that thread, David Chart posted the following:

Now that is interesting. To be honest, it does kind of solve the problem I was describing... But, I think we might house rule a different course as it does go against our troupe's reading of the section on page 173.

I think for our purposes, if you have need to fast cast (before your action), then you can't then go on to cast a normal spell. And I think there just needs to be a game balance rule saying that you can't fast cast in response to your own actions.

In a proper round with competent magi, one would simply have sufficient Parma to not worry about countering, just attacking and hoping to penetrate the other guy's MR first.

So boys and girls, don't forget to study your Parma and Penetration summae (no, adult films don't count for penetration advancement lol).

Hmph. I never saw that problem.

Perhaps D&D terminology would help.
In D&D, a character's turn in a round is devoted to a Standard Action. Like casting a spell - a normal spell, in ArM terms.
In addition, she can cast some spells as a Swift Action, allowing her to cast one such spell in addition to the normal one. This is a fast-cast spell.
In addition, outside of her turn, she may make an unlimited number of Immediate Actions in response to developments.

As I read it, a character may perform one Standard Action on his turn; magi often cast a normal spell. In addition, a character may make one Swift Action on his turn; so he can cast one fast-cast spell. In addition, the magus may cast more Fast-Cast spells as Immediate Actions, on other people's turns. (He must succeed in opposed Initiative checks to fast-cast.)

To answer the original question - yes, she can. She indeed needs to beat her own initiative.

I'd change the rule about Initiative, however. I'd instead simplify as follows: castingt the first fast-cast in a round has an ease factor of 6; the next an ease factor of 12; the next an ease factor of 18; and so on. If several magi fast-cast, the higher opposed roll wins.