I took the liberty, mainly so we can discuss it without further clutter of Arnau's thread.
So others know, the Batman reference comes from a saga Fixer and I were players together in a few years ago called "Novus Mane". Newly gauntleted young magi, Wirth and Roberto. Wirth is a Perdo specialist of the Apromor lineage, very stoic and laconic and intimidating. Onetime Roerto held a defeated pirate captain at the point of his flaming sword and flamboyantly said "Join us or Die", upon which moment Wirth rises out of the sea as a giant and says "I think you better listen to the man". Which isn't really Batman, but is iconic of his simple and direct style of intimidation. Other aspects inspired the Batman reference, such as having a wide variety of tick custom spells and his seriousness and his sneaky dissapearing with invisibility. Roberto's concentration duration invisibility spell is based off of Wirth's Diameter duration version.
Let's see. What else do I remember?
This is a valuable example to current and future players who want to revive a magus from a previous game.
Wirth has Roberto's original sword. The one he used from years and years and had since he was a child and originally belonged to his father Clemente.
Wirth had often demonstrated cool patience and from him Roberto learned to be less of a hot headed jerk. Cold hearted jerk gets better results sometimes
I suggest you swap True Love as a Major Flaw for Dependents, then take True Love as a Minor Virtue for free (transformed and and affirmed by your Matrimonial style Familiar Bond). I suggest you keep Book Learner. It is worth +35xp per Cycle and you will have at least two of them, maybe three. That is an additional 70 to 105 XP!
I forgot about the self-transformation focus. Exploit it
I see what you mean though. Puissant Brawl works great as a gained new virtue, but Affinity with Brawl is only really worth it if you have it from the beginning. And I wouldn't want for you to change any of those original virtues. The one that is the weakest link is Book Learner.
He was there hen we exposed Leolinus in Toledo. He was with Iolar and Roerto in Thebes where we fought the Witches of Thesally, he is the one that took control of the Dutch pirates in our harbor and turned them into a legit protection agency and lawful privateers. Fred Fischer and Johan VanHalen Senior work for him directly. I think his companion character was a warrior woman played by Andrew. Kilica Ozal. Fixer played the warrior Jan Axel.
...
I am rereading old Wirth stories
I took a look yesterday (but didn't have time to work more on him): I had swapped Book Learner for Puissant Brawl, and Improved Characteristics for Piercing Gaze
I kept the stats mostly as they were, only lowering Com to account for the loss of Improved Stats. A positive com didn't fit him at all, anyway, since he spoke so little, whereas Piercing Gaze is a good fit with his positive presence and leadership specialty in Intimidation ^^
The rest didn't change
I want him to have all kind of spells to modify himself, yeah ^^ And I want wings
Good times reading you recount all this. This was fun times
The Age of Innocence, where they had their adventures
Independance Day, when Novus Mane gains his freedom
A third act, when Florum retaliates in spite, or the magi of Novus Mane find themselves unable to face alone the challenge of the normandy tribunal, and Wirth relocates to Provence (waiting for Faith and Flame)
And at some point, he goes to a criamon on the path of strife for mystical training (gains puissant brawl, with martial ability block). Cause that's just cool 8)
A question: A MuCo spell to breathe underwater: Would it be on par with Eyes of the Cat, or require to change a Part of him into a fish (base 20)? A point could be made for both, depending on whether one thinks it's minor or not. And if people have some idea of similar minor MuCo abilities...
Too bad he won't be able to change into mist, but wolf and raven are game 8)
Someone posted what I thought to be the best, easiest, most medieval paradigm solution to the "shadow while invisible" problem. A MuCo base 4 spell, with an Auram requisite (IMO more appropriate than aquam) to give the body the quality of air that allows it to let light pass through. This is not invisibility, not at all (you still shed species and all), but, since you don't block light, you have no shadow, which, when you're invisible, give people a +3 malus to detect you (you still make sounds, leave footsteps...). Is this Ok by you? With both this and his "like a ghost passing by" spell, he expect to be quite hard to detect while invisible (+ 6 to EF, due to leaving no shadow and doing no sound). And one day, he'll learn Magus Incorporality
Roberto uses a Concentration variant of With's "Hide from Prying Eyes" spell.
Air still distorts light and creates shadows. Not much, like thin wispy clouds cause a bare shimmer or dimming. Hard to detect, but not impossible. ut you are only talking about a +3 bonus, so this seems reasonable. I would also accept adding an additional magnitude of Iganinem or two, or an Ignem requisite.
For the spell, not all air does. Clouds do. Fog, which are also auram, do, but the air between 2 magi doesn't, nor does the air between the sun and a magus.
So this spell gives that quality to one's body. Cast alone, you're not invisible at all, since you still shed species. But, since your body doesn't stop light, light can be perceived through you. Combined with an invisibility spell, this makes you harder to detect, since there are less signs, but not impossible, thus the +3 to detect.
There's no reason to add Imaginem or Ignem requisites, since it affects neither species or light, but if you want an additionnal mag for complexity, tell me.
the write-up:
"Makes a human body transparent, as though made of only air. This spell does not affect coloration or species. The resulting body can be seen through, but the muscles and organs are still visible as disembodied shapes of their appropriate color. This is often quite disturbing to most people (including magi) who have never seen such a thing. Originally intended to make invisibility spells more effective, it is also useful for studying human anatomy. Requisites for Forms of clothing and objects carried may be required. The shadow cast by a transparent body is thinner, weaker, and more diffuse, but still visible; increase the difficulty to spot a disembodied shadow by +3."
First, this'd be a Pe(Mu)Co(Im) spell, which seems kinda ridiculous
More importantly, these are 2 entirely separate effects, and I'm not so keen on the "pile on requisites to have one make-it-all spell", from an esthetic fashion, because I don't think spells should work like this (they usually have some unity of purpose and design) and because it leads to things like "learn 1 lvl 25 spell in one season instead of 2 lvl 20 in 2 seasons".
I also like the idea of spells that complement each others and build upon each other, this is something that at least some advanced magi should do, IMO*, and which shows they developped organically and sought to become better at what they do (which is the idea here ^^)
I've put some info on the wiki, more to follow, slowly.
The kind of ideas I'm developping for Core elder magi which, IMO, separate them from their younger brethren:
Spells and items that build upon each other, and complement each other. Ranulf is a great exemple of this, and this is probably the hardest thing to do here.
Spell Masteries: Elder Magi know their spells well, they don't botch, at least not on the important ones, and can do fancy tricks with them. After some years casting the same spells, you really should have some mastery in them.
Spells and items with custom ranges and durations: A cloak of invisibility that works only while you wear it (R: T, unlimited uses, Custom duration akin to While +1), this kind of fancy things that younger magi usually just won't have, being more "standard hermetic".
That is a plain MuCo spell if I ever saw one. No requisites at all. In fact I cannot see how you figured you even need requisites. It would be like asking for an Im requisite to a spell that polishes your armor because it is shiny now. Quite a disgusting spell this one, and will scare the hell out of A LOT of people to see your internal organs. Or their own.
IMO, it needs an Auram requisite because I give the body the "let light pass" quality of Air. Not unlike the various MuCo spells that require and An requisite because they borrow some quality from the animal realm.
I'm not sure about the organs being visible. I think they should, as, since light strikes them, they'll emit species (whereas, usually, it doesn't, then they don't).
Not really. Otherwise you start needing requieites for everything Muto easily and this is not how Muto works. You arwe making a body transparent, not giving it a propiety of air. In fact most MuCo(An) in the rulebook could be replicated without the Animal requisite. This is outdated legacy stuff.
I see your point. Note, though, that every MuCo spell that uses the "minor ability" guideline includes an Animal requisite, including later additions up to at least Apprentices. Taking a quick look at the spell index, most MuCo spells do use a requisite when doing things other than changing size/becoming tougher, mostly Animal ones.
This seems to indicate that, at the very least for the base 2 guideline, you need to add a requisite when adding/changing something non-human to the human form.
From memory, there are similar exemples, say, in MuHe, where you use a Mentem requisite to Awaken a plant, or a Terram requisite to make your wood as strong as metal, essentially giving it a property of Terram.
Note that your reasonning could also, if scaled, be also applied to Muto Corpus spells to become insubstantial, yet published exemple use an Auram or Mentem requisite. Likewise with, say, breathing fire.
The good point is that, as I see it, you could use this to give a body the hardness of metal, to get a higher soak bonus than normal, at the cost of a requisite.
I disagree with the official line, then I think this is a way to nerfg a MuCo specialist that only wants to improve his body. It is not you getting wings but raising the light sensitivity of your eyes, for example. or in this case changing one characteristic of a body. If I make a stone weight less with PeTe I do not need an Auram requisite. I do not see why do I need a requisite here. But if you want to nerf your own character, be my guest. Given the powr level of the saga I find this totally unnecessary but it is your batman.
I haven't looked at this thread for a while, but it seems to me that the principle here would not need to be linked to air- uncolored glass also casts no shadow. Now making the person look oddly (like colored glass, where you can see through them but also see them without invisibility) would certainly be appropriate, as that is essentially what they are doing with the spell (as opposed to using CrIg to banish the shadow)
Given that it can be a property of more than one element I don't think it should require a requisite (Jellyfish are transparent as well, that is animal, water inherently lets light pass, you can look through flames if what is on the other side is bright enough...), MuCo should suffice.
I think this is a way to nerfg a MuCo specialist that only wants to improve his body. It is not you getting wings but raising the light sensitivity of your eyes, for example. or in this case changing one characteristic of a body. If I make a stone weight less with PeTe I do not need an Auram requisite. I do not see why do I need a requisite here. But if you want to nerf your own character, be my guest. 
Given the powr level of the saga I find this totally unnecessary but it is your batman.