Aura Oscillation and Longer-Duration Spells

I was rereading Lion and the Lily the other day, and took a look at Carnac, with it's Aura that oscillates between Magic 5 (during the day), and Infernal 5 (at night). It's noted that despite it being one of the single most magically potent sites in Mythic Europe, no covenant has ever been established here, due to the combination of the oscillating Aura and the infestation of the Nain - who attack in groups, sometimes accompanied by some larger and more potent demons.

So, for a story seed, I thought of an ambitious magi (or, more likely, group of magi) who decides they're going to Cleanse Carnac.

There could be a lot of reasons for this: if cleansed, the vis sources here would likely make it one of the naturally richer covenant-sites in the region, giving it value from a political and strategic sense. The prestige alone for such a great feat of magical prowess would be immense for a member of Houses Flambeau or Tytalus, it'd be a potential source of original research for members of House Bonisagus, it's a sight of great natural beauty for members of House Jerbiton, and cleansing it would be prime Unique Quest material for various Mystery cults. (Also, a fantastic Archmagus challenge idea, if your PCs are at that level!)

I'm also aware that there are some spells in LoH (Conciatta's spells Dominance over the Infernal and This Heart of Darkness are practically tailor made to be used, if not alone, in conjunction with the spell designed below) that would be relevant to the situation - this sort of knowledge could be an excellent 'follow up' to establishing - especially because it's pretty easy to see the spell not being 100% successful, even if it does provide significantly (temporary) relief.

Cleanse the Land of Demonic Infestation (PeVi(Te) 35)
This ritual is designed to cleanse an area of demonic presence by destroying any Demons within the area. This is effectively a year-long duration version of Demon's Eternal Oblivion, that targets any creature within the area of the ritual, embedding power antithetical to demonic entities within the land itself. It will likely need to be cast in conjunction with a Wizard's Communion in order to achieve the extremely high penetration needed to deal with the mightier demons that accompany the Nain, but if cast with sufficient Penetration, it should constantly be removing the Might of Demonic entities within the land itself. (Base effect, +1 Touch, +4 Year, +4 Bound, +1 Terram requisite)

The idea here is for a spell that effectively does 5-10 (not great at math here) Might damage to demonic entities 'per round' - an effective way to go when you're not necessarily physically there. Obviously, this sort of spell could be seen by certain interests as "dealing with demons" - while it's destroying demons, it's certainly the kind of magic likely to stir up a bit of demonic attention in a way that more conservative groups in the Order may strictly Not Approve. I might not strictly need the Terram requisite for the anti-demonic effect, but it makes sense from a thematic perspective, as the demons appear to be 'linked' to the land - and could perhaps help the magic 'stick' a bit. Also, as a 7th magnitude spell, it would cause Warping to anyone in the area for an extended period of time - which could get some other complaints if the caster(s) aren't notifying people.

Obviously, a Magus/Maga is going to attempt to cast this sort of spell during the day, to take advantage of the wonderful Magical Aura of Carnac in the daytime. What I'm wondering about here is what happens when night falls, and the Infernal Aura rises. Obviously the Demons are getting a boost to their Infernal Might, and thus their magic resistance. But is the spell itself being affected, or is it considered to be already 'in place'? I've looked around for a bit, and haven't found a clear answer as to what happens to active mystical affects when an Aura changes, though this could just be my control-f fu being weak in this case. Cheers!

It's a bit of a jump to go from "destroys 5 points of might", to "destroys 5 points of might per round". I don't think that I'd allow a magic dispelling field spell that wind of mundane silences it's target every round and I'd treat your "demon killing field" spell the same way.

Instead of the ritual I'd craft an enchanted device that sends giant waves of demon's eternal oblivion cascading over the landscape every round in varying directions. It better fits with my aesthetics and it's less questionable from a rules perspective.

I like the setting behind it, but agree with Eric here. If this showed up as written in our Saga, I think it would do 5 points of Might damage... then nothing. Until the demon entered again, which would do five points of damage. It would do this for each demon entering, each time they entered the effected area.

Another reading is that it only reduces the demon's might for one year due to the duration. As Momentary Perdo spells are permanent, but non-momentary Perdo's target returns at the end of the spell, in this case a year. If this was the case you might be able to argue they can not recover that Might for the entirety of the year...?

Also, I just finished Against the Dark reread, and started Lion & the Lily last night .

I have it pretty clear because I made that same mistake: Might stripping spells with duration longer than momentary don't repeat their effect each round, but rather maintain their effect for the duration. It's tricky to find because it's not either on the PeVi guidelines or on the Vim section, but on the Duration one:

Just replace Terram with Vim and pit with Might: such a spell would remove 5 or 10 might points from demons and keep them unable to recover them for the duration.

Which makes me think about Grip of the Choking Hand; I think it would keep the target unable to breath, and so suffering deprivation rolls, instead of getting one fatigue level loss per round.

Think that such spells would make dealing with powerful creatures an easy cake: just create a level 10 PeVi with D: Diameter, get a nice penetration multiplier, go to cast it to the big dragon of might up to 60, leap of homecoming back to the lab, and return in 2 minutes to collect if not the vis at least the beast's treasure.

Khelek's post had me review the exact same section of the text, but of course I missed "rather than having its effect multiple times within the duration". However, there's also "A fire created with duration Diameter burns for two minutes, and may inflict damage every round over that period." This seems to apply that for Creo effects that themselves cause damage, these effects can be effective damage multipliers when given duration, but the same is not true for Perdo effects. (Which does seem a little biased in favor of Creo spells in combat, but c'est la vie)

I suppose I could go for a significantly higher potency version of the same spell that would trigger once for people entering the domain, and crank up the power so that it could destroy the Nain outright rather than draining them away. If we get it to the point it can handle a ~20 might demon you've essentially solved the Nain problem. I could also go for a potentially Re or Mu(Pe)Te(Vi) type effect that imbued the land with inherent anti-demonic properties for the year - I'm imagining a ritual that results in all the various Mehirs shooting out anti-demon blasts, similar to Erik's suggestion. I'd been leaning towards a ritual rather than an enchantment partially because it 'feels' like a single grand magical act to me more than 'took out my portable demonic radius-nuker and set up camp.' Also you can't do boundary effects in devices without either breaking the limit of creation or Hermetic empowerment - the second of which could have pretty severe side effects in an infernal aura.

That said, back to one of my original questions: Would the casting total of a big ritual be 'effectively weakened' by the change from a magical to Infernal Aura overnight? I'm under the impression that the casting total wouldn't be and the main worry is the increase in effective infernal might of the Demonic forces.

Would still love more input on effects/items to solve this, though!

What about using the Recurring spells/effects section of the Merinitia Mystery Spell Timing(HoH:MC, page 100-101)? Would that work?

The Bjornaer Sensory Targets would be useful, but can't be enchanted into items. Although a Verditius confraternity of bellmakers having T:Sound for enchantments as their special initiation doesn't sound too far fetched.

Here is my idea made into an actual item. I used x and y as variables because I'm not sure what level would be appropriate for your uses.

If you've lots of magic theory you could use red coral but the diamond + the agate get you a fair bonus.
I choose a weird environmental condition for triggering it so it isn't easily turned off even if the demons could figure out how to do it.
I made it sturdy so it's not easily destroyed
I pulled the size of an standard individual breeze out of thin air

Pro infernal characters could construct wind breaks or steal he item, both could make good stories.

An alternative that would work and be a lower level than my example device is a ritual that caused infernal creatures pain. That might fit within standard hermetic magic even though there is not an explicit guideline for it.

I was under the impression that I'd only get get the higher of the two (diamond and agate) since you only get the highest applicable shape and material bonus... But yes, red coral best. (And considering I view the whole thing as an archmagus sort of feat, the high MT seems more likely.)

Still, really appreciate the input, this is a cool one. Anti-demonic breezes! Perhaps some Rego Aurum effect could be used in conjunction to keep the breezes circulating within the area to increase the 'incidence of effect'!

Seeing your statement, I looked to find if the magus was restricted to a single shape bonus and a single material bonus. This quote from page 99 was the closest I found to answering the question

This seems to indicate that you can use multiple shapes and materials for bonuses to a lab total (capped by magic theory)

I was (probably incorrectly, now that I think about it) extrapolating from talisman attunement bonuses, where only the highest bonus applies.

PeVi 45 - Arc | Year | Boundary | - Exorcism of the Haunted Forest, Ritual
Infernal creatures within the affected area need an extra might point to use their infernal powers and lose one might point per day while within the boundary if this effect penetrates. If the infernal power was free before, they now need to pay the toll. Staying within the boundary, at least half of the year, puts the fiend’s might score at risk as they will need to roll a stamina stress die of 9+ or have their score lowered by one by the end of the year. Fiends may exhibit an array of symptoms that depict the discomfort of being subject to the effect of this spell such as being moist, hot to the touch or, for the more enduring of them, none at all. In order to establish the boundaries for the ritual, 5 arcane connections need to be gathered. The ritualist can then place them properly to form a pentagram that will define the limits. Taj experimented in an successful attempt to reproduce the effect of also affecting the targets each time they re-enter the affected area such as what he was able to design within “The Haunted Castle” spell. This spell was designed to cover the Infernal Fey forest that once resided near the town of Paphos.
(Arc +4 | Year +4 | Boundary +4 | Base 1 (General +2), +1 Size, +1 Toll)