And I wince at seeing all the typos above 
. Another attribute of this text interface is that it is very difficult to edit large messages.
Actually, I thought I was trying to beat the bomb's initiative.
If I remember correctly, you can only fast-cast a spontaneous spell or a spell that you have Mastery in Fast-Casting.
That being said, is it safe to say that being fairly certain that there's an invisible hand attached to the wand, and that the hand is in turn attached to a person of some kind? If so, she is going to try to spont a CrIg spell to torch said person. Base tbd (depending on how high she rolls – the more powerful the spell, the brighter he'll burn - but hopefully at least a 4). R: Voice(+2), D: Momentary, T: Individual, for a beginning target level of 10. Her CT is Sta 2 + Cr 10 + Ig 11 – Fast-Casting Penalty 10 = 13 + die roll (or 23, if this falls under her Focus), plus a die roll.
Her Fast-Casting speed is Qui 1 + Finesse 0 + die roll of ) = 10, and I think she needed to beat a 5, but I'm not sure.
Assuming that she gets that "counter-spell" off, her CT for the spell is 13 + die roll of 8 = 21, halved is 11 (or 31, halved is 16). It may not do any damage (since it probably won't pierce his MR), but it should at least distract him.
And on her normal turn, she is going to PoF him: CT 33 + die roll of 4 = 37, succeeding by 17. Her Penetration is 17 + Penetration 0 (really, PB?) = 17.
And the fact that her clothes are hanging in smoking tatters on her body, and she had to take deep breaths to get her fire out, may be a distraction, too 
.
You had to beat 9, which you did 
You are using 4th ed spont rules. In ArM5, you predetermine everything about the spont, including levels dedicated to penetration. Which would not have worked anyway.
He makes a concentration roll...
invisiblecastle.com/roller/view/3787497/
He rolled a 7, plus Concentration 3, equals 10. He succeeds in discharging the wand. It is designed to penetrate high Parma. Pietro fades into twilight. I will roll that out later (at library).
Now the form of the invisible assailant is outlined by the smoke and flash of fire that hit him. I don't know if it is kosher, but I will allow you to target him anyway.
And you are in luck. This guy isn't a magus, just a henchman. Covered by parma and turned invisible and equipped with a magic item. The guy Pietro zapped was similar, just a henchman with a device.
So, with the reduction from shared Parma, he cannot resist the spell.
Torched.
Damage = a SD + 15
invisiblecastle.com/roller/view/3787499/
7, plus 15 equals 22. Soak of only +1 equals 21 points of damage. That is, lemme count here...
Dead. You killed him flat out dead! He screams and fries to a crisp.
Carmen does something else hopefully useful. But this isn't about her. It is about YOU.
[color=blue]Good job! she shouts, and goes zap zap zap at her targets.
Then, right at that moment...
p. 81 of 5th edition says that "The chosen effect may be open-ended." In this case, base effect, no penetration, with the "open-ended" part going toward more damage. That's what I was going for, anyway.
One down, God knows how many to go, Vibria thinks, and...
((I'm half expecting a "Dun dun dunnnnnn" here ))
Actually, this is the moment Guillme pops in, if he so chooses.
I have been thinking about your breath power. Basically, Penetration. My thought is that it should be based on your Art Scores. It stems from a Hermetic Virtue, so it makes sense (and works great against invisible opponents). Your thoughts?
As for more invisible opponents,
you don't see any 
But this outdoor cafe is like a scene from Jackie Chan flick. Just stuff going on everywhere!
((Cool! Can I do the "throw booze in the air and light it on fire" trick? ))
Go for it 
Mythic Blood already has Penetration (it's Effect Level + Penetration = 30), and I had originally figured it as Level 20, Penetration 10. But looking at the spell creation guidelines, CrIg for 20 damage is Level 15, and if it's R: Personal, D: Momentary, T: Individual, that doesn't change the level any. However, if the Rego requisite that allows her to project her firebreath outward adds a magnitude, that brings it up to 20.
It does make sense, though, that as her knowledge of Creo and Ignem grow, so would her Penetration. Conveniently enough, her Creo and Ignem add up to 21, halved is 10 if you round down. How does: "her Penetration with the Dragon's Breath is half of her Creo + Ignem, rounded down" sound?
She's going to take a quick look around to who's fighting whom (and, if she's lucky, any clue that there are still any invisibles running around). Anyone who's fighting one of Pietro's guard is a target. If they're at range, she's going to start spitting Pilums of Fire at them.
Awareness Roll to see who to target: Per 0 + Awareness 3 + Keen Vision 3 + die roll of 9 = 12.
Casting roll for Pilum of Fire: CT 33 + die roll of 3 = 36; success, with a Penetration of 16.
I am going to run with a little narrative.
Everbody is kung-fu fighting...
Vibria blasts one, Carmen takes out another. Back to back, fire and lightning.
Someone tries to jump you, and you exhale a gout of fire in his face. Someone tries to grab Carmen. She does the Wizard's Leap. Then someone throws a net at her. Fast Cast leap. You torch the guy.
Your perception roll was good, and what you percieve is that attackers seem to be trying to incapacitate or capture Carmen. Not doing a good job. This "Spanish fire drill" is evidence that this wasn't very well thought out.
You, they are trying to outright kill you. Bot you are a fighter. Someone comes at you with knife in hand. You melt it. And the hand. Another stabs at you from behind. Too slow. You deliver a kick to the gut and finish him off in style.
The attackers are rapidly loosing, but they fight on like crazed fanatics.
But they seem to have lost what little magic resistance they had...
Yeah...Brawl: 5, Single Weapon: 4.
Gout of fire to the face, his hands fly up in pain, the knife goes flying, Vibria grabs it out of the air, cutting, burning. At one point, while the Bad Guys are laying back to decide who's going to kill themselves next, she takes the knife, spits on the blade (Blade of the Virulent Flame), grins, and motions "Bring it". Stark naked the whole time.
((Too bad we don't have the old GURPS Martial Arts "Bulletproof Nudity" rules ))
Awesome!
You are certainly gonna cause these guys some, um, distraction.
This plan didn't work out at all the way the unkown advesary(s) intended. So only one thing left to do.
Kill everyone.
Unfortunately, they already played that card. So the only option is to kill the remaining henchman.
All enemy combatants suddenly drop dead.
The civil authorities of the city start to arrive. You are standing there naked holing a flaming knife.
Lucy, you have some 'splaining to do!
This does not look good, Vibria thinks, and they probably won't believe the truth if I told them.
She casts Tremulous Vault of the Torch's Flame quickly to have the flame jump onto her, then sets the knife blade onto something non-flammable.
Are clothes you're wearing considered R: Personal? ("the casting magus or things that he is wearing"). If so, she sponts a CrHe (base 1, +2 for finished and treated products, R: Personal, D: Sun +2, T: Individual, for a target level of 5) to create a robe right quick, with a CT of Sta 2 + Cr 10 + He 0 + die roll of 8 = 18, halved is 9.
If not, Cr(Re)Im to create illusory clothes that move with her. Base 1, R: Personal, D: Sun +2, T: Individual, for a target level of 3 (or 4 if the Rego adds a magnitude). CT is Sta 2 + Cr/Re 5 + Im 0 + die roll of 8 = 15, halved is 8.
Once she's had her modesty restored, first thing she does is go check on Carmen (Int 1 + Chirurgy 2 + die roll of 4 = 7, or 8 if her Specialty of Burns comes into play.
After she's checked on/treated Carmen, she will check on Pietro.
She will be aware of the gendarmerie, but will ignore them unless they bug her.
I think RH Personal counts for clothes you are wearing, if you are wearing them. With a loud voice and exaggerated gestures you get +2, so a level 10 spont is no problem.
I should point out that there is no discernable aura at the cafe. Strange.
So you cloth yourself. Carmen does need medical attention. She took a big risk fighting on despite her wound. So you attend to her. And the city guard is poking around the death and destruction. A pair approaches you. One address you in Latinus (Mozarab). You can barely understand, and percieving that, the other speaks with heavilly accented Catalan
[color=red]Please come us with please
Pietro is nowhere to be found. Twilight zone.
When the guards confront you, Carmen gives you a grin and winks.
[color=blue]The Q's are gonna be p-o'd as it is. Time for plan B?
[color=red]"Ready when you are," Vibria says as she grins back.
Guillaume appears beside where Carmen had been a moment and a few Wizard's Leaps earlier. Fire flies about him as he tries to gain his bearings. A moment later he fast-casts Wizard's Leap himself to avoid becoming charcoal, moving to a shaded side of a nearby building. Once there he surveys the scene. Seeing they have the fight in hand and that the guards are coming he casts Cloak of True Invisibility (fortunately not botching but tiring himself - not more than 6 botch dice, right?) followed by Maintaining the Demanding Spell (25). He'll look for an opportunity to approach Carmen to whisper, "Guillaume Flambonis is here."
Well time for B-2
Carmen was planning to grab hold of Vibria and cast this around them, but then she hears a familiar voice. And his choice of words confirms it. Not many magi she knows uses "Flambonis". But the Latin geeks at Doisettep insist on it, and Guillme says it all the time.
So Carmen casts "Circling Winds of Protection" forcelessly. Those with MR are unaffected. But the guards are blown back. Then she fishes around for her pouch and discovers it fell off when the strap burned.
[color=blue]Crap! Pouch, over there on the ground. Key inside. Arcane Connection. Meet us there!
Camen casts Wings of Soaring Wind, grabs Vibria, and soars off back to the townhouse.
The strength of the wind is sufficient for two girls (one being petite (Carmen)); but the strain will cause her wound to worsen.
Unless someone wants to institute a plan C, and quick!
(Not off the top of my head).
[color=red]"Damn, I wish I could turn into a dragon already," Vibria mutters. She watches the wound carefully (not much else to do), and hopes that wherever Carmen is taking them is close.
Guillaume walks over, grabs the pouch and key, and walks to a secluded spot. He rests there a few minutes before casting The Leap of Homecoming (failing the first time and succeeding on the second.