First, does the Mercurian Magic efficient use of vis in rituals include longevity rituals?
Second, how common is it to be able to know rituals that are too big to cast yourself and need a Wizards Communion? Surely between applying two abilities to the casting total but only one to the lab total, ceremonial casting, extra vis use and the 10 point margin of error it is far more likely that a magus can cast bigger rituals than she can actually learn.
Longevity rituals are a tricky spot. We debated this for a while. In one of the supplements it says something to the effect that the first time it is a laboratory thing and afterward it is a ritual thing. However, I believe you have to spend the same amount of vis in subsequent uses of the same ritual. So if I'm remembering it all correctly, Mercurian Magic shouldn't help.
First, I'm not sure what the 10-point margin of error you're talking about is. You might want to double-check ritual magic.
I see a few issues here without respect to the lab total:
As for the lab total, I've found it relatively easy to get a much higher lab total than casting total:
So in the end it's like comparing the bonus from either Philosophiae or Artes Liberales to your assistants and your laboratory bonus, which generally favors the invention. But then you can miss by a fair amount with a ritual, which balances things back out if you don't mind sleeping a few days away.
Chris
That's what I meant - I forgot there was a difference between missing the total with formulaics and rituals.
Good points, I think the improved penetration is especially telling.
Just a note: Aegis must not penetrate to be effective.
But T: AC death spells aimed at Deidne do.
Not to derail this, but can you give a reference for that? If you want to argue about the wording of the spell itself, then you could say the same about Circular Ward Against Demons. Skimming through past posts I also quickly came upon at least one person who states such a lack of penetration is a house rule he uses. In our saga it always dampens but we require it to penetrate to keep beings out, and I don't think that jives with the rules at all.
Chris
Common rookie mistake (no insult intended).
You can often stack boni on your lab totals like nobody's business.
I have several characters who have learned spells they have essentially no chance of casting.
In our Constantinople saga I play a Jerbiton who happens to know Mercurian Magic. When inventing spells from a Lab Text in his Lab which has a massive bonus in Texts specialisation, not to mention the Form and Technique he is currently pursuing rituals from, he can easily learn CrCo40 healign rituals, but struggle to cast them. Sure, his Artes Liberales + Philisophiae help a lot, but he still risks being fatigued. And if he ever wanted Penetration? Forget about it.
It happens. In my troupe that happens from time to time. Wizzie commie is a very common spell around here. Generally the guy that wants to cast the impossible ritual also knows wizard's communion and/or has a lab text for it so others can help him cast it. It is not your everyday's bread, but it is far from rare.
CHeers,
Xavi
Only that it doesn't fit in hermetic magic since it's a hermetic breakthrough of Notatus + the description of it.
Compared to that, circular ward against demon totally fit in hermetic magic theory.
Funny, I've never, ever seen Wizard's Communion used. I wish we did use it though, I like the idea of it. Also, i play a Mercurian Magus and by not using it I feel part of his Major Hermetic Virtue is wasted.
BWT What if 2 magi cast a huge ritual together using Wiz Com, and one is Mercurian and the other isn't - what is the vis cost? Full? Half? 3/4?
In communion there is always a leader. As long as the leader is a mercrinan, the cost should be mnercurian. The pother magi casting the ritual are just sidekicks to the hero
Sadly the RAW disagree - all participants must have the virtue to get the vis break. I am disappoint.
Yeah thats what i thought.
Really? That will teach me not to post rules when at work 
Or not 
Xavi
Or it will teach you to have PDFs in your Dropbox
My what? What is a dropbox? Sounds interesting
Xavi
Dropbox is without doubt my favourite program ever. It is in essence a program you install on two or more computers that synchronizes files put into this folder. The files are also accesible on the net, if you log on with a computer on which you don't have this program. Then you cna just download the files. I use it to store my Ars Magica pdfs and my Metarcreator files so I can work on it on my home computer and while I'm at my workplace. I often have an hour or two from the end of a normal work day to the time my various sagas start a couple of times per week. So I use that time to update characters, write stroies etc. And I never have to worry about having the newest file, it's always just the one in the dropbox. Plus it's a backup is the computer crashes.
Also, you can share a folder with other Dropbox uses. I have a folder I share with my co-Alpha SG in my two sagas, here we store common character files for metarcreator as well as the covenant/library file.
It's super! You can even log onto Dropbox on the net and recover deleted files, altough only a limited amount of time backwards, but at least a month.
It's free and you get 2 GB, if you want more you can get it by paying. You can also get more space by inviting others. If you PM me and write your email, I can send an invite with a link which is simple to click and install from. You can then go on to invite your friends and co-gamers so you can share folder and files.
I can second the recommendation of Dropbox - I don't use it extensively, but it works fabulously. Do take ultraviolet up on the offer of an invite - I think there's a storage cap bonus for the inviter.