So as a moderate beginner ST I introduced a long term villain who is a fairly powerful demon (might 35 against a spring covenant). He has various machinations that include trying to bring an even greater demon into being (loosely following a demon story in "Thrice Told Tales"). As per the rules on true names in RoP: Infernal, I considered the demon to be strong enough that with good Infernal Lore resources they could discover the true name of the demon. They found a good source through some fun role-playing, and after 2 seasons, one of the Magi learned the demon's true name. Not realizing what a powerful tool I had given (again still a somewhat novice ST), they have now figured out that a Arcane Connection version of Internal Oblivion would have 5x penetration, with a momentary spell cast from the safety of the covenant. Undoubtedly they will now easily destroy this demon before the story has really gotten to the climax.
Now, I have no problem with their destroying the demon, despite my plan for a fun set of adventures around his goals. However, I just want to know if I'm missing something. With a level 10 formulaic spell, I believe, one caster can easily overcome the 36 penetration if he has a x5 penetration bonus. A few repeated castings would destroy the demon in under a minute. My first instinct is that I gave away the true name WAY too easily (which, again is fine for this story), but the infernal book implies that powerful demons often have true names that are relatively easy to find. Even if it were a 50 might demon, what keeps a medium powered magus from destroying it easily if he has the true name?
There's a couple things I might be able to contribute here.
First, an Arcane Connection version of Demon's Eternal Oblivion will be higher than Level 10. This is a +2 modifier to the spell, so a spell inflicting 10 Might damage will actually be level 20 and a PC will need to invent it. Now, that might not be that big a difference, but it might make the Penetration of your PC spell low enough that the demon can resist. At least, until the magi learn Wizard's Communion.
Second, I was re-reading RoP:I myself recently and was surprised to learn that demons, even those killed with Might-stripping spells, are not completely erased from existence. Their bodies cease to exist, but the demon itself is consigned to Hell, where it is presumably tortured and confined till the end of time. I presume this is true because Hermetic magic cannot break the law of the Divine, and only God determines what happens to a demon. Under normal circumstances, that's as good as dead, and my impression is that no demon ordinarily comes back from such a defeat. But the stories of your PCs are by definition un-ordinary, so I don't think it's out of the question that a demon they defeat and consign to Hell for eternity somehow returns to plague them another day.
Generally speaking - don't count on BBEG's MR to protect him from Hermetic magic. Magi can get very powerful, even without arcane connections (of course, letting them gather some is fun).
That's within the RAW. I personally like house rules. So...
I actually suggest doubling or even tripling the Magic Resistance conferred by Magic Might. I find this fits more into the flavor of creatures of Might as depicted in the books. If you had tripled his MR, the demons would have had MR 105 - which would have allowed him to feel the "ping" of summoning, say, and decide whether to come rather than to be forced to come. Notice also that while this MR may seem excessive, powerful magi can affect such a creature, especially with things like a True Name, wizard's communion, and of course raw vis.
RoP:I was written a long time ago. Since then, Magic beings got the chance to send off Aspects of themselves, and the Divine archangels and saints have similar mechanics so can keep hiding behind the Lunar Sphere and can't be directly targeted at all. I suggest letting demons, especially powerful demons, be likewise able to send Aspects of themselves to earth, and to make it impossible to affect them in Hell (except perhaps through special virtues like Cthonic Magic or Summoning).
Finally, one of my favorite house rules is to isntitute a new limit of magic - you can't destroy eternal spirits. So you can deplete a demon's Might and thus send it to Hell; but it will regain its power there in time, and will return (with a vengence...). Or you can bind the demon - but be careful lest someone, in time, breaks his prison. Or so on. But you can't destroy it.
This makes for much better story material, I think. And it works with things like the Titans, too (that's why they were bound in Tartarus aka the Magic Realm, rather than being killed off!). And with ghosts.
I am not trying to figure out that spell, the situation in which it might be cast, or the consequential MR of its target.
But wouldn't a major demon threatened with destruction in under a minute be a desperate and extremely dangerous opponent during that time? How many magus characters IYC could resist its all out attacks?
I would be skeptical of even a spell with a range of arcane connection affecting a demon while in hell- it may have to be summoned before it can be destroyed.
Of course they could put up a ward to contain demons, summon the demon into it, and then slay it... however the first demon is likely to try and show up and free the higher order demon when they try this, given the instinctual nature of demonic intelligence...
What are the consequences of destroying/banishing to Hell/otherwise removing Demon A? Will it stop Demon B from being brought to this world? Will it stop the other machinations? Will the various machinations run off in unexpected directions? If the demon has minions or cultists or deluded puppets, they may well take advantage of the power vacuum and fill it. If there's more than one in a position to fill it, they will fight over the position. If a moderately large group, it is likely to fracture and spin off troublesome groups.
Destroying/removing the demon solves part of the problem, not all of it.
That approach works well for Hermetic Magic vs. Might but makes it nearly impossible for other magicians to affect supernatural creatures or for creatures of Might to affect each other.
Fundamentally, the problem is that penetration is based on casting total and Hermetic Magicians have far higher casting totals than anyone else, due to the use of Art+Art rather than Art+Ability, compounded by the many virtues available to provide bonuses to Hermetics and their general ability to learn faster based on the shared Order of Hermes knowledge base.
This wasn't a problem in earlier editions of the game when non-hermetics could be dismissed as simple "hedge magicians". Now that rival forms of magic have become more important it has become a real bother.
Yep. The solution is simple, even if some find appalling - don't multiply the MR against hedge wizards, only against Hermetic magi.
While we're at it, however - you can also double the magi's MR, to make Parma more meaningful. And if you do, you can as an alternative to the above increase the Penetration of creatures, which solves half the problem (creatures now can penetrate each other's increased MR). Hedge wizards still get to not affect creatures, not without more house rules at least... I mostly don't mind that - you don't usually hear tales of how the Folk Witch turned the fearies into newts, but rather about how she bargained with them and turned the mundanes to newts. But YMMV.