OK, I'm having a brain fart - where are the rules for crating a ward against a targeted individual only? Ie, a ReVi Farie ward that affects ONLY the Lord of Ice?
Are you thinking of the Columbae in the Ex-Misc chapter of HoH: S? They have the ability to do that sort of thing, but it's not a standard Hermetic ward.
You could do it as an enchanted device or two, one effect to detect the target and one effect to do what you want to it.
It was the Columbae - thanks!
..which answers my question: "how do you create an antimagic ward that doesn't affect the casting magi?" You use Columbae Circle/Ring magic, apparently - and exclude the caster from the effect of the ward.
EDIT - actually, would that work? The magi isn't affected by the antimagic, but would his magic still be affected by it, seeing as it is considered separate from him?
No, his magic would not be affected either. You can always word it in more lawyeresque terms to achieve that effect, but no need to do that.
Why can't you just use invent a "standard" formulaic ward spell of the relevant form, but make it versus a particular individual.
For example, with CrTe there is a generic guideline that allows you to make metal. But this does not prohibit you from making a specific CrTe formulaic spell that makes a sword.
Likewise there is a generic ReTe guideline that allows you to ward against Te magical creatures. But this should not prohibit you from making a specific ReTe formulaic ward spell to ward against the Earth elemental that lives in the hills behind the covenant (for example).
Well, with the Columbae, I think they can do it on the fly - ie, they can take the general ward, and dynamically create the specifically-targeted one. (Reads the book) - ah, yeah: they can take general circle/ring techniques and add in restrictions on them, as they cast them. And in reading through the Columbae examples - yeah, it's pretty clear that you can say "All magic (vim) that is not my own". Thanks, Xavi!
Although - if a standard Hermetic can create a spell with an exclusion in it (ie, the generalist Perdo Vim anti-magic effect vs. everyone BUT the caster), then you've just created a functional, castable Shadow Parma.
If that's the case, then I'm all for it - but I'll need to adjust some of my character's enchantments that he's got planned for his familiar, is all.
Note that there's no warding against magic under the current Form guidelines (Parma is something different). This is made explicit in the core; Aegis of the Hearth is the closest someone got.
A ward is Rego, not Perdo. Sure, you can use Perdo Ignem to destroy a fire and thus protect folks from getting hurt by it, but then you have to target the fire, not the folks to be protected. Similarly, you simply can't cast a Perdo Vim spell on a Target that destroys all magic affecting that Target (even leaving aside the problem of excluding the Target's own magic - a problem to which Columbae magic is no solution, since it affects wards, and wards are Rego rather than Perdo spells).
The closest you could get would be to create an invested device that constantly detected magic affecting a person (Intellego Vim, with that person as a Target), and dispelled it as soon as it was detected (Perdo Vim, with the detected spell as a Target). It would just be an issue of magnitude to allow detection of whether it's the Target's own magic, and prevent the dispel from triggering in that case. Some obvious issues with this solution:
1.Perdo Vim can mask an incoming from detection.
2.If the caster's magic does not trigger dispelling, an incoming effect could be changed to resemble the caster's with an appropriate Muto Vim effect.
3.Incoming effects get dispelled almost immediately, but not before they affect the Target at least momentarily.
4.Being constantly subjected to the detection effect would eventually warp the Target (unless the Target spent at least half of his time "unshielded" etc.).
Re: the warp - yep. Hence the "put it in the familiar" comment.
And in looking at the core rulebook - The ReVi section doesn't say you can't ward vs. magic - it says you can't create Magic Resistance. That's the "Level of the effect subtracts from casting total" game mechanic. This is the "spells of X magnitude or less don't work, regardless of casting total" game mechanic. Is there another section that discusses this?
I was under the impression that Perdo effects, when made non-instant and covered a target, ended up as a suppression effect on any item that passed into their area. So a Perdo Terram Circle/Ring would destroy any stone that was tossed into it...until the circle was broken, at which all the destroyed stone would appear, unbroken, in the circle. Similarly, I was assuming that an antimagic effect would surpress any magic effect, up to its level, until the duration expired. If there were some effectcs that were lasting longer than the surpression (such as a Duration: Moon that was being surpressed by a Duration:Sun) - then the spell would start up again.
You don't "put" an effect into the familiar. You "put" it into the bond.
And its triggering must be under the control of either yourself, or of the familiar, not the bond.
Hence, a familiar won't help with a detect & trigger effect.
However, I had made a mistake here. You just need to make the detection spell one that gives a magical sense to the caster of the dispel, rather than one that targets the Individual to be "checked". So, warping should not be an issue.
[EDIT: On the other hand, maybe I didn't make a mistake. It's not clear to me if you can give an item a magical sense and have it react to what it e.g. "sees". That would require some basic mental capability in the item to "interpret" what it sees, unlike what happens with an Intellego spell telling a "yes/no" answer. It's an interesting question that never came up in our games.]
Still, there's no guideline for it, and in this case I would not assume it's one of those "it's not there but you can extrapolate it from others"-guideline.
Yes and no. There are two subtle issues here.
The first is that if your Target is Circle, (Room, Structure, or Boundary, you can attack spells that you can't otherwise detect because you are Targeting all spells in a (detectable) "area" - but if your Target is an Individual, it's an Individual spell, not all spells affecting an Individual (check the Vim guidelines: they say unless the opposite is stated, it's either one or the other for any given Vim effect, and for all the examples of the "dispelling" guidelines, the Target is clearly the spell).
The second is the much trickier question of whether a spell that targets e.g. Room affects all stuff that is in that Room when the spell is cast (potentially continuing after the stuff leaves the Room) or instead affects all stuff that finds itself in that Room only as long as it remains in the Room. The core has examples for both; but all the Ars products quickly started to use the first interpretation exclusively.
That's fine, but again, you have to Target the spell you want to eliminate. Which can do either with an area-of-effect Target such as Room or Circle, which has problems of its own, or by detecting the spell first. You can't dispel all magic on an Individual by casting a spell with that Individual as a Target.
I'm pretty sure you can, actually - look at the Disenchant ritual, for example, which destroys all of an enchanted device's powers. I don't think the fact that it's a ritual or on an enchanted device should change anything. I would allow an ongoing Perdo Vim spell which destroyed any magical effects on a person (possibly including their Parma, if they're not careful), but spells would exist for a moment first - i.e., it wouldn't have any effect on momentary spells, and any longer duration spells would effectively have a very brief impact.
I don't think the stone would come back (unless you have the flaw Harmless Magic from the Merinita section of HoH:S). My understanding is that if Perdo destroys something that can naturally not exist (such as a bunch of stone), then the effect is permanent, whereas if it destroys something that cannot naturally not exist (such as the stone's weight), it will come back at the end of the spell.
Strictly speaking, it's because it's a legacy spell.
But if you want to make it a little more compatible with modern magic theory, it's because it doesn't actually even attempt to dispel each power - it "attacks" the underlaying enchantment that binds magic into the item. For an invested item, this is what you establish when you initially prepare the item with Vim Vis. For a lesser device, this is build into the enchantment itself.
You will notice that the object becomes "in all ways a mundane object", meaning that if you wanted to use it as an Invested Device later, you'd have to re-fill it with Vim Vis.
You could ofcourse allow this, but to the best of my undersanding, you'd be houseruling. 
You can tell Tellus' master has taught him Puissant Magic Theory
I'll take that as a compliment, and say Thank You!
Yes, it was meant as a compliment! It was really well argumented.
And it vaguely sounded like the stereotypical question-answer I imagine one hears at a Bonisagus gauntlet.
The Vim guidelines do also say "The Individual target for a Vim spell can refer to either an individual spell or an individual object or person, and similarly for Group", though in the initial introductory text. I realise this was brought up earlier:
So my earlier mention of the Disenchant Ritual was meant as a counterpoint to ezzelino's statement. But combined with the guideline, I don't think it's accurate to say it's just a legacy spell issue.
I'll grant it's a houserule, but I think mostly in the details of exactly how it works, rather than that something along those general lines is possible.
Huh. Interesting. So I guess it's back to the timing issue: of whether or not PeVi effects can be in place, and cancel things out that are not inside the target of the spell at casting time.
...although the Rego version seems to indicate that it CAN do that, as it can follow the warding guidelines.
EDIT - although it could also be argued that warding is an explicit guideline for the different Rego TeFo combinations; and because ReVi doesn't have an explicit "Ward Magic Spell" effect (unlike "ward magic creature" - which it does have), then it can't be done under the current system.
EDIT II - although I seem to recall that the ReVi guideline is "suppress a target spell", rather than "suppress all magical effects" or "supress a type of magical effect" of the PeVi variety. So it may be that you can, in fact, create a suppression aura...for one spell.
Which would certainly be useful in some circumstances (Wizard's War vs. Intangible Tunnels), although if it really is "a single spell", rather than "guideline", then it's a superficial MuVi casting away from being pointless.
Exactly! Aegis is the closest Hermetic magic got to that.
This was different in previous editions - you could ward against magic with Rego Vim - but since it was a solution that tended to outshine Parma Magica it was removed in 5th edition.
I've always assumed (and always seen assumed) that it means that you can suppress any one instance of any spell from any guideline. So three different castings of same suppression spell could be used to suppress (i.e. temporarily "cancel") a given instance Aegis of the Hearth, a given instance of Mastering the Unruly Beast, and a given instance of Ward against flame - though in all three cases you'd have to target the suppressed spell.
You would not be able to cast a Ward against Mastering the Unruly Beast on your familiar.