I may well be wrong, but I believe it's currently sadly unclear. Which is why we're having this discussion.
Why/why not?
I would expect such effects to be stripped.
I suspect there are at least two types in that sentence? It does not appear to make sense in it's current form. If you meant:
I happen to think it is not only RAW but also desirable.
Oh, you left out one other related one that might be asked: what happens to your Parma Magica if you walk into a foreign AotH?
The exact post you're quoting, refers to dispelling the the Aegis, meaning PeVi, neither MuVi nor ReVi. PeVi has not typically referenced the penetration of the affected effect. So no surprise there.
It's actually in the same class as Longevity Rituals and familiar cords. "Other extant effects on a being protected by MR who enters the Aegis"
First, I do not think it's desirable for them to be stripped - see callen's example of the gorgon's eyes.
Second, I do not think that the Aegis explicitly overwrites the default RAW (which then applies): to dispel effects on someone, you must bypass their MR.
Let me add you break the global MR framework HARD badly if you break this. Sure, you can say "It's only for the Aegis because it's so super-special". But it's still very poor aesthetics and there are ways to make the Aegis stronger without resorting to this.
I wouldn't lump them together for a few reasons. First and most importantly, those other two are truly constant effects rather than temporary ones. Second, those other two normally needing special Ritual magic to dispel, while PM can be brought down with Wind of Mundane Silence, for example.
PM can be brought down by relatively simple spells like Wind of Mundane Silence, so it should be possible for AotH to pull it down. That still leaves the penetration issue, though. A neat aspect of considering this as an effect having to penetrate AotH is that PM would get brought down, along with many other things it might protect, but creatures like the gorgon would not suffer this same inconvenience. This allows for some differentiation between inherent creature powers and magi trying to shield things under PM. I know I still haven't provided much of an answer, though, more jus things to think about.
Regardless.
By my reading of the RAW, i.e. that you must penetrate a being's MR to dispel stuff on them, even if you are an Aegis, then:
I will answer from my groups arrived on consensus, even though in some places I disagree with it (though I will note where).
Currently my group plays that external "foreign" magic items must penetrate the Aegis and and internal ones suffer the reduction to Penetration. Though truly this is something I disagree with and should be added to the "How Does Aegis Work?" thread since it means only those with MR are protected from internal "foreign" magic items.
The Aegis reduction to Penetration effect works on magical creatures (beings aligned with the Realm of Magic or beings aligned with all Realms depending on interpretation), not just beings with Might. While Powers were not codified until after the varies Realms of Power books came out, this is what the effect is targeting. Innate magical effects which have a Penetration Total but no Casting Total. The power a Magus gains from Mythic Blood is a Power and thus suffers from Penetration Reduction. Skinchanger (and similar) are unaffected because we could not settle on something that did not completely block them. The closest we came was getting a positive result on a Sta + [Realm] Lore Ability - Aegis Penalty roll (with the Realm used being the one the power is derived from). This is something I pushed for since it made things like Skinchanger similar to Heartbeast.
We require already cast spells to be able to Penetrate the Aegis when crossing over into it. We view the external spell on someone crossing the boundary the same as casting from outside to inside, making no exceptions for spells on beings with MR. While a being with Might might be able to cross the boundary, all spells on them that cannot Penetrate the Aegis are stripped. The Parma Magica however is not stripped, since we ruled the Aegis is a "Parma Magica of Place" and two Parma Magica coming into contact will not negate each other.
LR and the cords of a familiar are part of the beings essential nature. The LR for example cannot be dispelled (this was an official ruling). The cords of a familiar are also not suppressed, though any effects enchanted into the bond are resisted the same as an enchanted item. Note that effects in the bond are activated by the member they do not effect which if one is inside and one outside becomes important.
Yes, this is the interesting direction thing I mentioned, though. Consider RAW with these two ideas in mind for ordering, not for simply being:
Now, what happens first? Is the magus walking into the AotH boundary the case that the magus is bringing an effect into the AotH so PM must penetrate AotH, or a case of something trying to bring down PM so AotH must penetrate PM?
As for "immediately," to re-raise PM, that would be 1 Diameter. But, yes, you could certainly raise it again. But a 2-minute vulnerability should worry you if you're at war.
Are you sure of that? There is a guideline that explicitly lets you dispel a Longevity Ritual:
(HoH:TL p.75) Gen: Dispel a specific type of enchantment... To qualify the spell needs to specify a particular Hermetic Form or a specific type of enchantment, such as... Longevity Rituals.
So, a "foreign" enchanted device activated within the Aegis, sees both a reduction of its penetration, and it must penetrate the Level or fizzle out? In which order does that happen?
(i.e. which of the two: a) first penetration reduced, and then it is compared to check for fizzling, or b) first the effect checks for fizzling, and if it survives penetration is reduced?)
There's a profound difference though.
PM stops stuff. If the AotH really worked like Parma, sure, it would keep a magus with "spells on" out of the Boundary, without making any of these spells fizzle. No doubt. But AotH does not work like Parma.
AoTH actively dispels stuff. When you say "For an effect to be brought into AotH, it [the effect] must penetrate.", that's just a mechanical representation. What's happening is really: "the AotH actively dispels any supernatural effect if some formula is satisfied". The supernatural effect is not acting on the Aegis, it's the Aegis that's acting on the supernatural effect. Thus, to act, it must first bypass the MR of the effect's target, if the spell is "attached" to a MR target.
Now, the general rule for MR is: in order to affect those protected by MR, via a direct supernatural effect, you need to first bypass MR. Unless I am mistaken (I confess I am too lazy to look), this includes removing from them effects that enhance their MR, like Parma, and in fact any effect "hanging" on them. AoTH, as written does not go around this general principle. I think protecting the sanctity of this principle is more important than giving an edge to the Aegis, particularly because one can give other edges to the Aegis.
The crux, however, is this.
A "stronger" AotH should be able to pull a "weaker" Parma down.
But a "weaker" AotH should not be able to pull a "stronger" Parma down.
If you assume that AotH:
a) (sensibly, in my opinion) affects all supernatural effects (e.g. it blocks a Purifying Touch just as it blocks a Hermetic spell achieving the same effect), regardless of them being "spells" or having "casting totals".
b) needs no penetration,
then the weakest Aegis (Level 20) can bring down the strongest Parma of the strongest Archmage (say Parma 15). I think this is undesirable.
You are correct, the ruling was that a specific ritual (one targeting LR) rather than a more general ritual dispel (one targeting a Form) is required.
I vote b). Makes most sense to me.
I think it the Gorgon's gaze should be unable to turn others to stone within an aegis, just like a dragon should have troubles breathing fire. Otherwise, just call the snakes in the Gorgon's hair the Monstrous Appearance inferiority rather than call it a constant cosmetic personal power. Virtues and Flaws aren't suppressed by the Aegis, and I'm not sure why you would spend virtue points to buy a constant personal power that makes you ugly.
I think I at some point had the idea, that a foreign magic item inside an Aegis har a reduction in Penetration equal to half Aegis level AND that if the item's Penetration is reduced to less than 0 it won't work at all. I like this better than using both a Pen reduction plus another check to see if it fizzles.
Plus I'd to the same for creature powers
Mythic Blood Powers have Penetration (or may have, it cna be 0 if you like). For them I'd do the same as with devices above: Reduce Pen, if less than 0 then it fizzles. Effects like SKinchanger could just be viewed as having Pen 0, which they fizzle in even the puniest of Aegis
No, the Parma of the foreign magus is irelevant, the Aegis acts just like casting spells at the Aegis from outside or spells bringing things inside.
No effect for Longevity or Familiar cords, these are as itegral to a magus as the Gift, and the Aegis doesn't affect this. Familiar powers however function like devices or other creature powers - except I don't recall if a magus can add extra levels to a familiar power for Penetration?
But should it cease to be able to see out of all of its eyes and have its Perception lowered as a result? The reason it's a Power rather than Flaw is that it provides a Perception bonus up to +6.
To make you fearsome!
That said, I also agree that the Aegis should curtail your ability to affect others with your magic... like a powerful, constant WInd of Mundane Silence. In fact, it should do so more effectively than it currently does, because for several classes of effects, you can still affect others easily, even if your effect is very weak and the Aegis very strong.
But a being's MR, if sufficiently strong should provide shelter from that "wind of dispelling" on that very being. E.g. a being who's puissant enough to walk into an Aegis and is immune to fire, should stay immune to fire if the Aegis is too weak to breach its MR. A being whose watery form is held together by magic should not collapse because it entered an Aegis that was too weak to keep it out!