If a spirit doesn't make itself corporeal, what options are there for a magus to kill it so that they can harvest its vis? To my knowledge, the standard Might-ripping spells don't leave any vis behind to gather.
Depending on the spirit mentem or aurum- most would be mentem. Or the form associated with the spirit. In theory you simply try a spell to extract the vis directly- Rego Vim resisted by the spirit's magic resistance.
I thing that this effect could work:
The Invisible Maw:
MuMe(Te) 50
R: Touch, D: Solar, O: Room
This effect transform any spirit on solid statue, so after they could be destroyed making possible harvest his Vis.
(Base 25, +1 Touch, +2 Solar, +2 Room)
Or maybe one Rego Form to order materialize one spirit. (Base 5 to control it, maybe the duration it's need it)
I thing that this effect could work:
The Invisible Maw:
MuMe(Te) 50
R: Touch, D: Solar, O: Room
This effect transform any spirit on solid statue, so after they could be destroyed making possible harvest his Vis.
(Base 25, +1 Touch, +2 Solar, +2 Room)
Or maybe one Rego Form to order materialize one spirit. (Base 5 to control it, maybe the duration it's need it)
So, potentially...
Tear the Essence
ReVi(Pe) 35 (Base 10 + 4 Arcane Connection + 1 requisite)
R: Arcane Connection, D: Mom, T: Ind
You remove and gather all of the vis in a Magic spirit of 35 Might or less if you get past their resistance, destroying the spirit itself.
Why would this be so much easier than PeVi(Re)? Or, in other words, should destroying a spirit while also taking its magic be easier than destroying the spirit alone? If you look at destroying 35 Might via PeVi, I would expect this to be one magnitude higher for the extra effect handled with a requisite. That would be a base of 25, iirc. So I would say this spell should be ReVi(Pe)50.
Fair enough.
Since spirits have stats like size and strength with each other, could one use an attack spell that targets the bodiless spirit and then cast a ReVi spell to transfer the immaterial vis remains?
For example:
Aetheric Spiculum
CrIg(Me) 25 (Base 10 + 2 Voice + 1 requisite)
Deals +15 damage to a spirit without a body.
It would seem to be a Hermetic version of ablating which extracts vis only...
Is that a bad thing or good? What about the version of destruction (Aetheric Spiculum) that doesn't mess with their vis?
Dealing with spirits in this way is skirting the boundary of being infernal in nature, though skirting is not the same as crossing. Someone who has a reputation for ablating spirits (or other spirit-related magics) is probably going to attract attention from the kind of special-interest groups who keep a close eye out for infernalist practices, regardless of the specific methods they use.
Note that ablating itself, while an infernal power, is not strictly in violation of the Code. That said, it's cutting a very fine line. A pious or overzealous lawman (quaesitor, hoplite, whatever) might well decide it's not worth splitting hairs in tribunal and go for the more expedient solution of Wizard's War.
So in short, it's no more or less a good or bad thing than any other serious delving into spirit-related magic.
But on the nature of vis in general...
It is also worth noting that many spirits tend to leave behind some kind of mortal remains or something when they are defeated by non-might-draining means. These are typically where the creature's magic coalesces into vis, which the magi can then run off with.
Vis as a game mechanic is originally derived from the idea of monsters having loot. So a magical critter that doesn't drop easily usable loot (easy enough that 'gather the essence' should be sufficient) is possibly the SG just setting the game's challenge higher. Personally I'd say that if the group can legitimately deal with the critter without resorting to might-stripping, they should get to keep the treasure without needing specialised, high-level spells to do so. YSMV, of course.
Back to the original question: what options are there to kill spirits that don't turn material? Can you 'just' add a Mentem or Vim requisite to your Pilum of Fire or whatever to harm their immaterial bodies, or do you need to do something else?
That's going to vary hugely by spirit. What works for a ghost probably won't work for the spirit of a river.
Ghosts can also often be laid to rest by resolving whatever is binding them to their ghostly existence - and typically leave behind a nice vis prize for doing so.
Spirits of things can often be 'harmed' by doing something unpleasant to whatever they represent.
You could also try muto-ing the spirit into a corporeal form then blasting it, though that may or may not work as intended.
For a guaranteed-win, straight-up extraction of power from a still 'living' spirit, ablating is probably the best option. There's also spirit empowerment if you're looking for vis to power rituals. But given that all of these things require virtues, it's probably fair to assume that purely hermetic ablating/draining is probably going to require a breakthrough.
I might be referring to an old version, but I believe in Broken Covenant of Calebais, when the PCs were confronted to one of the ghost magus, they could resort to Imaginem spells to interact with him. I believe they could even damage her that way (was it Drininkanea ?).
What was the logic behind this to work, I cannot remember and I don't have the book at hand.
I would personally authorise Mentem, and specifically PeMe the same ways at PeVi destroy demons. I don't like that Vim is the universal solution against any supernatural creature - but it is beyond the initial question.
Lay to Rest the Haunting Spirit PeMe Gen, ArM5, p. 150 - so this certainly works on Ghosts.
We house-ruled that PeMe, like PeVi, strips might and thus leaves no usable vis.
We also house-ruled that if you use a form-appropriate spell, that spell works regardless of the realm to which the target belongs. Thus, PeMe will destroy magic-ghosts, fae-ghosts, infernal-ghosts or divine-ghosts without having to have a different version for each.
It keeps them competitive with the PeVi spells.
Interestingly, we have both the same rules.
And we do the same. Technique + Vim affects any creature of a specific Realm regardless of Form. Technique + Form affects creatures aligned to than Form regardless of Realm.
Mark
Same House Rule here.
So if you know the form, you can destroy it irregardless of realm? And if you know the realm, you can destroy it (via PeVi) regardless of form? Makes a certain amount of sense.
Edit: Regardless, when it comes to infernal and such corruptions of natural creatures, yes you can strip their might away, but unless you destroy the physical body, it's still a dangerous, agressive creature trying to kill you.
Take a hell hound. Strip it's might. it can still chow down on your succulent tasty tasty grog-flesh. And a magus without a grog is vulnerable to the mundane servitors demons like to keep.
It gets iffy.
If the hound is a demon who has a hound-shape, then the demon is going to evaporate when it runs out of might because it's still a spirit, it's just coagulated into a hound-y form.
If the hound is a dog with infernal might, then stripping it's might (can you even might-strip a non-spirit?) is going to leave you with a nonmagical, large, probably black and likely very aggressive hound.