I'm having a little trouble determining technique/form and level for a particular spell.
The basic principle of the spell is that the mage holds two small, round stones in his hand, and casts the spell on a human target. For the duration, the target now sees as if the stones were his eyes; he cannot see out of his own eyes nor can he control the placement of the stones unless the target somehow gains possession of them.
The stones would, although being magical and temporarily arcane connections to the target, otherwise be normal stones, and touching/hitting them doesn't hurt the target (although it might be very disorienting).
Is this a ReIm or a MuCo spell, or a bit of both?
What would the appropriate level be for a single human target at Range Eye and Duration Sun? Should it be an Individual or Part target?
What would the appropriate penalty be if, say, the mage cast the spell and then immediately chucked the stones into tall grass, or off of a waterfall?
Are there any other limitations I might be missing, such as ending the spell by breaking the stones (as opposed to fragmenting the image seen), whether taking the stones out of sight range ends the spell if not cast with an arcane connection, or something else entirely?
MuCo. You're not affecting the species, but rather the sense and that's associated with the body. Or possibly the mind - I confess that I have difficulty wrapping my head around some of the ideas in A&A.
Well, you're making a significant, unnatural change to a thing. Making a mind physical is MuMe25 as the base and making a human solid stone is MuCo25, so that seems reasonable. I don't think Part is required because a sense is a discrete thing to my mind, though under the Form of Corpus. As such, you're looking at MuCo 40 for Eye and Sun. The victim is almost certain to pick up massive warping as well.
None for the magus. For the victim? I'd say treat them as blind, since only an idiot would keep their eyes open (which, to my mind, is necessary to see, regardless of where your sight comes from) with that sort of chaos around them.
Breaking the stones should end the spell, since a sense is indivisible. The range that the stones could travel in the duration is immaterial, however. If you cast a Sight range spell on someone, making their hair pink and spotty, and they teleport to Durenmar, their hair remains spotted.
Thinking about it, you could probably achieve a similar effect with ReIm, transporting the species from the stones to the victim's eyes, blotting out their normal vision. This is almost certainly likely to be easier to cast, but not as flavourful to my mind.
Mu(Re)Co, I'd say. With hefty finesse, or high level. You're transforming and magically moving a sensory organ. Oh, wait, that would switch the stones and his eyes, which might not be what you're looking for.
Cr(Mu)Me + tethered magic, perhaps. (consults A&A) Rewriting the target's common sense (i.e. the sense integrating the external senses) into ignoring his real eyes and only showing what hits the stones. Tethered magic to hand off the effect to the stones and not the caster. Yeah, that would work, I think.
I think that there are probably several ways to acheive this effect, depending on what the magus is good at, but one possible solution is, I think, below.
I think that it could be achieved by a In(Pe)Im(Co) effect, i.e. InIm with Pe and Co requisites. The effect allows the target to use his sense at a distance (that is InIm), but it also destroys his normal sight, so Pe and Co requisites needed --- possibly Me instead of Co if you imagine that sight is to do with the functioning of the mind rather than the functioning of the sense organs.
The penalty to the person who now has difficulty seeing where he is? The same penalty as for being blind.
I don't think that it matters if the stones move from the target after the spell has been cast --- the Range only matters when the target is initially affected.
As to breaking the stones --- that's something that needs to be sorted out in spell design. I think it would be entirely reasonable to either end the spell if the stones are broken, or let the sight fragment into facets (which would be very disconcerting). The spell could be made to do either, I think.
Hmmm, I'd have to say that distinction is purely semantic. Surely one cannot sense magically unless one has acquired a magical sense.
The Target by definition provided by the OP seems to be the person's sense of sight which the spell is transferring to the stones so as to enable him/her to see where he/she is not. If that IS the case then surely their must be a Target:Vision requirement. The reference to Range:Sight leads me to believe that the OP and others are falling into the common trap of mistaking Range (range to Target) "Sight" with the Target:Vision.
The former would allow a spell to be cast on a Target as far as the caster could see, the latter Targets a sense which is intended to be modified in some way as appears to be the case with such a spell as that above.
So I would likely rule that it would require In(Mu)Im(Co)(Te) with no cost for the requisites as they are intrinsic to the desired effect of the spell, but that Range must be + 4 Arcane Connection and Target must be +3 Vision resulting in:
The Absent Witness
In(Mu)Im(Co)(Te) level 30 (minimum)
(base 1, +4 Arcane Connection, +2 Sun(or more if the stones are to be viable at great distance), +3 Vision
Allows a magus to transfer his sense of sight to two small stones which may be carried far from the magus so that he might observe events without being bodily present. The magus (or other subject) is rendered blind to his immediate environs for the duration of the spell once the stones are carried away.
Not so, in this case. An InVi spell, for instance, with Target Vision gives you a new sense, which is treated as sight. In the case of the original spell, it doesn't grant a new sense; it affects an existing one.
The Range:Sight, in this case, was first suggested as a limiting range for the spell, such that if the stones were taken out of it, the spell would fail. Nice and flavoursome, but not necessary.
Why do people want to invoke Intellego here? Intelleo grants information which may, by means of the sensory targets, be understood using an existing sense rather than by affecting a single target as with Touch. The spell effect required doesn't grant any information - InIm as a method of scrying just determines what species are present at the target. Likewise, why is an AC needed? An arcane connection is needed to affect a target that cannot otherwise be sensed - in this case, we are assuming a pseudo-combat situation and so Eye or Voice are more useful.
Why Perdo? The sense is being replaced or displaced, not destroyed. The purpose of the spell is not to allow the target to use his sense at a distance (which is nominally ReIm) but rather to remove it from his body. It's a subtle but important distinction. To compare it to the equivalent using the sense of touch - allowing me to touch at a distance lets me move my hands and feel the surface of a table on the other side of the room. Moving my sense of touch to the table, however, means that I feel what touches the table.
This can then be more or less achieved either with ReIm (moving the species from a thing to one's sensory organs, overriding or displacing the species which would arrive be there) or MuCo (actually displacing the sense from the body). Arguably a Te requisite is required to tether it to the stones, just as an An requisite is required to turn a mind into a bird.
Where it gets complicated is that the spell has, effectively, two targets and possibly two ranges. The victim's sense (which may be a Part or an Individual in its own right) and the stones which are the receptacle, and thus Eye and Touch. The current rules don't really support this, except in as far as a shapeshifting spell with an animal hide focus can be ended by removing the hide.
InIm is being used because the RAW guideline box explicitly says for base 1: "Use one sense at a distance". Thus, like Eyes of the Eagle (which allows one to enhance his/her sight beyond the natural capacity of man) the Target should be the Vision of the caster. He wants to send his sight ability into portable stones, he MUST Target his Vision.
First statment is incorrect, the purpose IS to allow the caster to use his/her sense at a distance (which is NOT normally ReIm but ALWAYS InIm as you wiould see in the core rule guidelines). That he desires to do so by transferring his sense of sight entirely to the stones only corroborates your second statement.
You seem to be confusing the sense of sight with the species that sight might perceive. Nothing in the OP's original premise aims to effect any species, only how species are sensed (and where).
I would like to have my try about this interesting spell.
I see many ways to do this, with similar tough notable differences. I will try to be as close as possible both to the RAW and to the exact effect that you demands the spell do.
I don't see any Muto effect here. That would be giving the stone the ability to see. Nor any terram effect. The stones are merely a way to describe how the spell works, it's cosmetic; it could be apple used, it wouldn't change anything to the effect.
I would hesitate between a combination of Rego / Perdo / Intellego, Imaginem / Corpus or Mentem.
I think the effect here is about the same as "teleporting the eyes" away. At 5 paces (about eyes range) it's Guideline level 10, with Target: Part, for a total of (BASE 10, eye +1 magnitude, sun +2, part +1) ReCo30.
Note that it also return the "eyes" back when the spell expire, which is different from the exact guideline, but very similar. You could add a magnitude for that, if you feel it should.
The fact that you teleport only the seeing ability away into two stones, and not the actual eyes, is purely cosmetic (and cool) effect. It is really the same, only the internal working of the spell change from the exact Guideline. This is, IMHO, a proper use of the spell guidelines: finding the appropriate guideline(s) to the effect you want.
Also, it doesn't add magnitudes or a requisite in Te, as the stones adds nothing to the spell effect.
Now, teleporting the eyes away would mean, er...normally.. , that the eyes can't see anymore. (think about it =P ). So you need an Intellego Imaginem requisite, as noted by other people, for them to be still seeing from the two stones.
The way to calculate a requisite is to design the added effect all by itself:
As noted earlier, this spell have similarities with the Guideline of InIm 1: use one sense at a distance. Compare with a Summoning the Distant image, InIm25, but without the hearing: (a InIm20)
But, there are 2 things different from that last spell: #1 it doesn't see/target a particular room, what is seen is not a fixed thing or place, so it targets needs be Vision,
If you leave target: individual, then the person whose sight is teleported would only see the stones, or the like. #2 it grants the sense to another person. (at Eyerange)
So : Guideline level 1, +1 Eye, +2 Sun, +4 Vision. Total for the requisite: InIm20.
This last effect is of lesser level than the previous effect, adds to the effect of the spell, and is less than level 30. So you should add +1 magnitude and In and Im requisite to the ReCo effect.
Base level: 10
+1 requisite (the InIm effect)
Add In and Im as requisite arts.
Eye, Sun, Part.
(the Vision target for the requisite effect is not taken into account at the final target, only the "main" effect is. If the InIm would be of higher level than the ReCo, it would be a In(Re)Im(Co) spell, with Target: Vision)
Effect: as you wanted!
This is well described in Houses of Hermes: Societates p. 33. Blinded, relying only on sounds, give +9 attack, +9 defence, and +12 stealth.
If you aim at confusing the one affected, with some surprise, I would give the same as Confusion of the Insane vibrations, (ReIm30, p. 147; -3 att, -3 def, +2 botch dices) but only for one round, since he can probably realise what is going on and close his eyes or the like (The penalty depends a lot on the roleplay of the target).
If you design the spell to oblige the recipient to see, I would go for an added botch dice and minus 1 on all checks.
You are not missing anything regarding the rules. Those questions depends really on your choice and how your troupes play.
I would tend to allow that breaking the stones ends the spell, as this is very intuitive. It's balanced, this has advantages and drawbacks. It's cool. (RAW permit this only in MuCo, see that guideline box)
A Pe(In)Co(Im) (about level 35) spell could destroy the eyes if you crush the stones. I would demands the stone to be an arcane connection to the person or his eyes to be able to crush them like that from a long distance away.
A ReIm spell would teleport the species away could do it too. But the problem here is really great, because such a spell would actually targets different species as they come "into" the eyes. The spell would keep casting itself again and again until the duration expire. Also, given the variant amount of species that could be moved, maybe you would need a boost to size and target: group. This could be possible by the RAW, because there are already such exception, but I would not advise this thread of thoughts, unless you do not fear it's impact on the spell design.
As a Story Guide, I do not allow easy eye contact in an ordinary combat situation. The eyes are a social thing IMO...
From my understanding, the organs of the senses are a physical "ability" in Mythic Europe. So it's Corpus and not Mentem. (but this is in some way in contradiction with CrMe which boost perception... this is another part of this debate)
Just a case of multiple ways of achieving a similar effect.
Sure, you can somehow "move" the target's sight to the stones, in which case I guess maybe a Re or Mu Technique would be appropriate. I was thinking more on the lines of destroying the target's original sense and then creating a new sense based in the stones, in which case the Pe requisite is to destroy the original sense.
Either way should work. You get much the same result. Which version a particular magus would pick, would probably depend on how good he was at the various Arts involved.
In fact, it's not entirely clear what happens to the character's original sense when you just use a vanilla InIm effect to see from a distant location. Can you also see from your actual location? Or does the vanilla InIm effect "transfer" the character's perspective to the new location. If the later, then you would only need a InIm spell to achieve the effect (no requisites).
Well, the scrying examples from the core (Prying Eyes or Ear for Distant Voices, for instance) do not use the sensory targets - the spells simply reveal (presumably as knowledge gained) the species at the target. Whether or not that overrides the sense of the caster is presumably a flavour effect determined by the caster. Seeing, for want of a better word, both at once is presumably disorienting unless you close your eyes, and will make you miss details in both.
Those spells which let you detect a thing such as Sight of the Active Magics which use Vision target effectively allow you to cast the spell on everything you see. The basic spell would be touch range and provide information on that target only directly to the caster's mind, rather than filtering it through a sense. There's also the question of whether blinding a magus removes his ability to useSotAM.
It's also worth noting that Intellego spells specificly affect the caster, and granting such a sense to another is a Mu(In)Me effect. The spell in question is targetting a victim, though I agree that there are multiple ways of doing so, Intellego is not required for any of them.
ReIm would be easiest, but I think the MuCo would be the most fun, if difficult, since by turning the sense into a rock, damage to the rock should logically damage the sense. Throwing the stones into a fire should burn and thus destroy the victim's sight, where as with the ReIm spell, it would just dazzle them and probably cause nightmares for a while.