Hmm. Taking into account Art & Academe, these effects may indeed be impossible under current Hermetic theory. There is a shape there to target, but no substance to affect.
That's no obstacle to using them in a non-hermetic/mystery artefact, though. Some cult or non-hermetic can easily have non-aristotle modes of thought that allows them to target shadows with their magic. YSMV.
After reconsidering, that's exactly where I'm headed too, WoC.
I like it, but I'm not sure I'm convinced. (Not nearly as sure about my initial position either now, tho', admittedly!) 
Shadows are certainly not Imagonem - that is only the illusion of a shadow. (But since shadows are 2 dimensional and purely in the visual realm, the differences between a natural shadow, a magical shadow, and an illusion of a shadow are grey and debatable. However, they are parallel to the differences between normal touch and the illusion of touch - there is still something missing in the magical version, even if it's not perceptible, and independent regarding whether we have proper terms to describe that diff.)
Terram is not defined as covering { a stone wall, or the hole in the wall } - but Ignem is defined (as WoC points out) as covering { Heat (or cold), or light (or dark) }. Or at least that's how I remembered the rules reading.
However, in re-reading them carefully (see sig), Ignem is not "darkness" and "cold" - the phrase used is "...spells that result in cold temperatures (and, by analogy, darkness) are possible through Ignem". It doesn't come close to saying that you "create" these end results, just that you get there via Ignem. If there are 4 elements, "darkness and cold" isn't one/aren't two of them, just as "sere dryness" and "vacuum" aren't paired elements with water and air.
In Aurum, if you create "a bad smell" - that's Creo, not Perdo - you don't "destroy" fresh air in that sense. (That could be achieved thru Imagonem as well, and again the diffs are subtle and arguable, but there are diffs.) So unless you can "Creo" a shadow - a real shadow, not an illusion of one - I don't think anything is there but a contrast to what would have been otherwise. You don't eat a "hunger" to feel hunger in your belly*, there is no tangible "loss" created when something dies*, and nothing makes a bunch of "silence" in the middle of the night* - it's just that what otherwise would be there, isn't.
(* Note that this is not true in every fantasy world model, but it seems to be for canon Hermetic magic. Some models are far less formulaic , far more "word play" dependent, that if you can say a thing, it exists. Fritz Lieber and Ursula LeGuin (Eathsea, etc) jump to mind on those scores.)
So I'm starting flipflop and to lean toward "shadow" as being a relative absence, not a "thing" in and of itself, at least in the Hermetic model. Altho' the hole in the wall is a fine analogy, I'll suggest instead Perdo Vim - if you PeVi a spell, you do not then have a "not-a-spell", a "negative spellness" that you can then keep as a pet and adapt to nefarious, sophistic uses.*
[i](* No, not "sophisticated" uses - [u]sophistic[/u] uses - look it up.)[/i] :wink:
However, in genre, "darkness" is certainly a "thing" that can be controlled by some types of wizards - so perhaps this is simply not a Hermetic effect? The archetypal evil sorcerer conjuring shadows (not illusions, but actual "things of shadow") to put a crimp in someone's social calendar is a classic. But maybe this type of "shadow" only accidentally shares its name with the thing that follows us around on sunny days? Maybe in AM these are things more of the demonic- or spirit-world? Or... something outside Hermetic Theory (if not Hermetic limits?) That part would be much less canon defined as to what that sort of shadow "is", and much more Saga dependent.
I like this effect - it's a classic, if an extremely powerful (and appropriately high magnitude) one. It's creative, and shows a good understanding of the Hermetic premise of Techniques. However, I think I'm changing camps - I don't think "shadows" are legit things to affect. Not in Hermetic magic, sorry. 
Imaginem does not necessarily create illusions. It also manipulates real species.
Creating a shadow can be PeIg to me, but manipulating it beyond the "make it lighter or darker" area, will be Imaginem for sure. YMMV.
Cheers,
Xavi
Yes, but then the question is "what is a shadow?" And "whatever I make it look like" is not the answer.
The only "species" I believe can be manipulated are those emanating from the "perceived thing" - in this case, a dark area. And that "emanation" can be altered, as could any image, but that does not alter the thing itself.
To actually affect the shadow itself, you'd need to manipulate the light (or lack of it) that is causing that shadow - and that's Ignem.
In this sense, species are acting like an echo - Ignem affects the initial Form that causes the effect (light), but Imagonem can only affect the return of that effect to the senses. The original sound, or the original shadow, is unaffected by Imagonem, even if it appears differently to the person perceiving the echo/image.
(If I understand "species" correctly, which I may not. If I'm not, if one of the more erudite on that subject could link me to an approp past discussion, that'd be appreciated, thnx!)
In general, I would use my usual highly detailed technique of nailing chamber pots: you can use Intellego Animal or whatever to manipulate it if you convince the rest of the troupe it is OK to do so. 
In this case I would say both Rego Ignem and Rego Imaginem can manipulate a shadow.
Xavi
Generally, I would say I'm convinced by the above arguments that shadow is absence of light and therefore cannot be controlled as such. A ReIg spell can still manipulate shadows, by manipulating light. A MuIg(Te) effect, however, could not target the shadows - only the light.
I think emptiness goes well with the Infernal. I think I'd allow anyone with Cthonic Magic to command the emptiness of light with Ignem, the emptiness of the stone wall with Terram, the emptiness of a spell with Vim... That sounds like a cool NPC there. And summoning demonic shadows is fine too; perhaps with PeIg instead of ReVi? Yeah, all sorts of nice options there.
Of course, YSMV.
Magi of Hermes, page 135, section Attunements states that “darkness” is “light's absence”, and thus justifies a whole battery of PeIg-spells in the same chapter. There is no detailed specification of what shadows really are, nor whether they are more than mere patches of murk or darkness. However, since all effects related to darkness are produced by PeIg-spells, it is likely that a Mythical shadow's coming into being (I intentionally avoid the term “creation” due to its misleading similarity to Creo) is related to this Technique/Form-combination.
Admittedly, this assumption does not clarify whether the usual Mythic Shadow, either mundane or magical in nature, can be tapped into and manipulated (Re), be transformed and converted to substance (Mu), or, by the expenditure of vis, even made permanent by Hermetic magic. The discussions I remember about this topic usually ended in this being either extraordinary complex, and thus hardly feasible for a casual real-world magus, or even beyond the scope of Hermetic magic.
Well, we were not very sure which art to choose for the manipolation of shadows, in the end we opted for Ignem reading what is written on the PeIg guidelines:
"Destroying something's shadows is thus CrIg, or possibly ReIg, not PeIm."
That is why we excluded Im in favor of Ig, however I think we'll follow the suggestion of Xavi and allow the use of both.
This is not an option in our game, a player has a verditius with a magical focus in darkness as character and I don't want to break his toy saying that he can no longer do his little games with shadows...
In Magi of Hermes there's Ranulf of Flambeau that with his magical focus with unnatural fires can do wonderful (and wierd) things, the player wants to do the same things with the manipulation of darkness and as a group we decided to allow it.
This is a good suggestion, I think we'll go with it.
I still would appreciate some guidance; putting aside the shadows, how to manage a giant made of stone created and controlled by a magus who tries to hit an enemy protected by MR? What would be the damage inflicted?
Hi,
I am saying that no shadow is created, though a shadow is caused.
That's right.
In the same way a "lack of animal" does not fall under the form of Animal, a lack of light or fire is not Ignem.
I'm not saying that it's creating darkness, but the image of a shadow. CrIm can create the image of a black cat, yes? So why not a dark figure that looks like a shadow?
I believe you refer to something different, that an object whose image is PeImed still casts a shadow.
No. PeIg is a process through which light is destroyed. PeAn isn't an "unanimal." PeMe isn't an unmind. The absence of mind and animal cannot be affected by Me or An, respectively. Dark and cold are two conditions of the lack of Ignem.
They're not. I can cause shadows to appear through PeIg, and I can cause shadows to shift by using ReIg to manipulate a light source, but I cannot use ReIg to manipulate shadows.
Cold and dark are deprecated compared to heat and light.
Yes. That's what I mean above: A spell to directly create a shadow is CrIm.
You can do odd things to them as Imaginem. They are not covered by Ignem, as I attempt to explain above.
To recapitulate: I can obliterate a stone using PeTe. But I cannot then use Terram to manipulate the space where the stone had been, though I can CrTe a new stone. In a similar way, I cannot use Animal to manipulate animals that aren't there, or use Ignem to manipulate a shadow, which is the explicit absence of Ignem.
Anyway,
Ken
But PeIg also creates cold, also the absence of ignem. And ReIg/MuIg should affect cold, because nothing else can... So no reason for it to not affect a shadow as well, which is also the "negative" side of Ignem.
If we go on on this track, how many other things can we come up with that can no longer be targeted?
No, a shadow is a reduction/absence of light. This makes it fall clearly under Ignem. Otherwise it is impossible to control or change cold just because its the absence or reduction of Ig.
Agreed. Because it makes at least some degree of sense and doesnt kill off playability.
Thats restricting yourself to being unable to directly control light. Which is what Ignem DOES already.
But a shadow wont be the lack of light 99% of the time... It will be the relative reduction of light.
And PeIg is used to get... cold...
Meaning that you can use ReIg to manipulate shadows...
No, but a spell to create what looks like a shadow is.
Irrelevant as there is no such thing as "un-animals" or a partial lack of animal. There IS such a thing as a reduction or partial lack of Ig.
No, its the relative reduction in OR absence.
ReTe base 10 hurls a stone with enough force to do +10 damage. So +10 per shadow? (HoH:S pg 38)
Yes, but this is potentially MUCH bigger than a 2nd magnitude effect. The shadow can be size x10 of a large bonfire, so... well, see below.
Heh, last I checked, "lack of animal" is Perdo Animal. What, you think that's another Imagonem? If you can't sense it, it's not there? ("I'm not listening to you! Nanananananananana!")
It worries me that you don't hear what you're saying. It's the image of a shadow, it looks like a shadow, but it's not a shadow. No more than an illusion of the moon or sun are the moon or the sun, or an illusion of a dead animal is a dead animal.
And if you think "the image of a shadow" and the shadow itself are the same thing, that's the same as claiming that "the image" of anything else made with light and color is the same - the sun and moon, the night sky... Sorry I don't buy it, not for a second. 
The beam from a distant lantern is mere species, but the flame itself is not. The shadow is not emating species as brightly as the area around it, but those species are not the shadow any more than the above "intangibles". (limit of celestial sphere aside.)
Yeah, and you should really read all of a thread before posting and beating a dead horse. I've already flopped on this point to some degree, and already covered of the points you attempt to, so... yeah.
Now, in an effort to get back to the question in the original post...
I'm not sure you'd be "breaking his toy" - I'm not sure he's not trying to get some necromancy (or some rough equiv) in through the back door.
The question is - "What is a shadow?"
If it's something like "A relative low light area with clear boundaries, caused by a physical object, often a creature", then that's fine - and that's all it is.
If it's something like "An animate, intangible creature of the undead or anti-matter realm", then "darkness" doesn't cover it. That's necromancy.
However, it's also true that in genre, a person's "shadow" is seen to have some potential for... well, "some life of its own", for lack of a better term. And that's a grey area, and each author, each story, each game must define that as best fits.
So for my money, "darkness" doesn't cover "undead shades", or anything close to them, regardless of some overlap of the word "shadow" or "shade".
Also - I'd be very leary about a player who claims that "If I can work my Major Focus into a spell definition, then it's covered!". Conjuring a wolf and then turning it into a massive CrIg effect via "MuAn(Ig)" is not covered under "MMF: Wolf" imo, and once a "shadow" turns into stone it's no longer "darkness", nor even close (and just turning it into stone is pretty questionable imo). If you want to run a high-powered, no-reins saga, that's your call, but I'd think long and hard about what sort of precedent and long-term repercussions this decision would have (including for future character builds!).
I replied to this on the first page; will repost here, with some afterthoughts added in, in some attempt to steer this runaway train back on track...
First, upon reflection it's not clear that Rego can turn a 2 dimensional shadow into a 3 dimensional one (especially not in the same effect that merely moves it around). That sounds like a different Muto effect, similar to turning a mind into a bird, etc. It's a distinctly unnatural change.
Yep, sure, absolutely, I completely agree.
Couple/few ways to approach this, and they should all be considered and balanced against each other...
If it's more "man sized", you still have stone "fists" hitting fast - at "dancing" speed. A mace is +8 (+ attack roll bonus), a warhaul +12 (+ etc.) - somewhere in there, using Finesse as the attack roll (with penalties for multiple simultaneous opponents).
b) By the Level of the Effects (not the item, but the effect that item generates), you've got an initial Level 20 effect, then modified by a level 35 effect, and then augmented again by a level 40.PeIg 20 (Base 3, +2 Voice, +1 Conc, +1 Part, +1 Size)
ReIg 35 (Base 10, +2 Voice, +1 Conc, +1 Group, +1 Size)
MuIg 40 (Base 10, +2 Voice, +1 Conc, +1 Group, +1 Size, +1 Requisite) There are no guidelines for adjudicating such, but that's going to be some kinda powerful. Compare to the largest core book effects, and it should easily outclass them by several "magnitudes" of unpleasantness.
iii) Game balance. Sounds like whoever created this is something of a stud, so they're already operating in the upper atmosphere. But don't be a slave to the rules and find you've just written the demise of your saga. (Alternately, letting a lesser mage find this thing won't guarantee they can figure out how it works, and the creator may find it's so powerful that the Order comes and speaks to him about how he's been using it...)
All that said, if it's one BIG shadow, I think anything it hits is beyond "soak", unless it's equally magical.
The dragon in the core book (p 194) has is size +8 and only +20 damage, but it has +22 attack, and that latter can add directly to damage. This "stone shadow" won't have a big attack, but when it hits it should hit like the aforementioned 10 tons of bricks. +30? +40? More?
In Hermes Portal issue #14 (can be downloaded for free online) there is a spell to animate a stone statue. You might look at it. It is fairly powerful. We have based Severin's Carved Assassins (from TOME) on it (reducing soak slightly) to get a playable animated statue
Cheers,
Xavi
The player intends to manipulate the shadows through magical effects capable of changing radically their nature (turning them into solid three-dimensional forms for example), I just wanted to say this.
Sorry but I disagree, in both cases the targets are wolves that are covered under the Focus.
The talisman of Ranulf for example (MoH page 114) has two effects instilled:
Topiary of Flames -> re-shape a fire into a shape desired by the magus
Flames of Stone -> change the target fire to hard as stone, it is specified that Ranulf create temporary structures in combination with the effect above
Well, both the effects are covered under his focus (otherwise his lab total would be too low).
I don't missed your reply Cuchulainshound, it contains very useful suggestions but I just wanted more opinions if possible 
Thanks Xavi! The Walking Statue spell is just what I was looking for.
(I figured as much, just trying to prime the pump back to the OP, and also added a few after thoughts.)
Yeah, I'll admit I have a narrow interpretation.
I just have a problem when someone uses some Focus as an "excuse" for every other magical effect out there. The above-mentioned explosion really has nothing to do with wolves or Muto Animal, and everything to do with Creo Ignem. - it just uses the "wolf" part as an excuse to get the Focus bonus. It's turning a wolf into any and every magical effect out there, and that's not the flavour a Focus is supposed to give imo, nor the breadth a focus is supposed to cover, especially if it's a "minor" focus. It's Hermetic fission and abusive imo, but not every saga is so limited, nor should be.
Mmm, the first 2 spells isnt a problem but the third doesnt really have much to do with "darkness" or "shadows", so i would lean towards not applying the focus there.
But noone said it was...?
Once you turn the wolf into flames, the wolf shape becomes irrelevant however, then a "wolf" focus would no longer apply. If you have a wolf with flames shooting from it the focus still applies to the wolf, but not in any way to the flames and the spell to cause the flames would also not be covered.
And if you turn a wolf into flames, you do get the focus but then you get to play with several requisites instead, which is probably worse anyway.
The same logic applies to cold, yes: cold is defined by the absence of heat, and controlling or changing cold can only be achieved by manipulating it's opposite, heat, which is governed by Ignem. Thus, one cannot design spells that target the cold, say, to change it into smell, because cold is defined by a lack of heat, and is not something in itself.
This problem only affects Ignem, as none of the other Forms have a definition for what their absence brings about - unless you are willing to say the Mundane is the lack of Magic, and therefore Vim, which would basically mean Vim can manipulate anything not magical.
There are a few ways this issue can be interpreted to suit individual sagas, such as:
A- As explained above, since neither cold nor shadow can be defined as something that is, only as something that is not, they cannot be targeted. The caster cannot be aware of them to target them, for he doesn't know what they are.
B- Instead of being the absence of heat and light, cold and shadow are aspects of Ignem on their own rights, and thus affected by it.
C- As B, except they remain impossible to affect due to yet another failure in Bonisagus' Magic Theory.
D- Once a shadow is created it is governed by Imaginem, much as when water is frozen it is governed by Aquam.
EDIT: Sorry to beat a dead horse, as pointed out earlier, but I thought the interpretations might give people other ideas on how to solve this in their saga.
VERY valid points about Shadow not being able to be targeted. However, since the GM doesn't want that because of his player (careful here), I shall leave it aside.
A note, especially in regards to CH, which seems to have overlooked it: The 3rd effect doesn't change Shadows into stone, but make them as hard as stone. So, in effect, all it's doing is making the shadows solid enough to strike.
Some thoughts:
The 2nd effect, IMO, is Re(mu), or even maybe Re(Mu, Cr): As someone noted, not only are you making the Shadows move under your command, but you're also making them 3-dimensionnal, divorcing them from the medium they're projected upon, which is highly unnatural. This is, in act, 2 things: a a rego effect to move the shadows (could be done on the ground), and a Mu(Cr) effect to make them 3-dimensional (like creating a shadow castle from a shadow)
For the damage, I'd say it should be comparable to the Projector's damage. I mean, if a giant strikes you with a mighty club, his club will feel as hard as stone to you as it pulps your face. Would this be different for his hard as stone shadow? I think not.
For imaginem... As far as I understand, species come from the light exciting something, which then project species. So a shadow, darkness, should be the way an object appear when not projecting species? Like, the invisible magus still blocks light (even though his species are destroyed), thus it doesn't lights the ground, which doesn't project species. So I say Imaginem has nothing to do with shadows, although it can create false ones.
Agreed, with the exception that things like "I create a fire that has a wolf's shape and hurl it at my ennemies" should NOT benefit from even a Major Focus
As I interpret the thing to change a wolf into flames would apply the focus, manipolate these flames with additional effects not, maybe you are saying the same thing.
I'm aware of this, these effects are "thematic" not more powerful, I know that would be a lot more effective take a terram specialist with a magical focus(stone) to rise giants and temporary structures
Hmm, maybe you are right. We took as reference the aforementioned effect Topiary of Flames that is only ReIg, but in this case the shadow became something of radically different and these requisites are appriopriate.
Here I'm missing something, what do you mean exactly?