One of the magi in my saga, who has just passed gauntlet, is a Vim specialist. We just ran through part of Calebais, giving him an opportunity to try out Perdo Vim spells as well as see what happens when a spirit leaves behind Vis after "dying."
He has asked about the possibility of something like a Perdo Vim spell with a rego requisite (or some other combination of techniques and forms) that would reduce a target's might score, but retain the vis after the creature passes on, or transfer the vis to another vessel as its extracted, or something along those lines.
He also suggested the possibility of it being two spells ( one to reduce the might, and a second to "capture" the dissipating might as vis. Being a "metamagic" type character, he's good at things like counterspells, fast casting, and such, so this approach appealed to him, but he was ok with either.
Since we're all new to the system, each pc in the adventure had some spell level xp from apprenticeship unspent, so they could experiment with spont. spells while adventuring and cement them into formulaic spells as they became more familiar with the magic spells, retconning their character sheets as it were.
At that moment, he had a good story reason to want to be able to cast such a spell - his familiar
I've tentetatively ruled that:
a. This effect should require a ritual. But that's stupid, because rituals use vis, making the transaction nearly worthless, unless you've got a very low-level might-stipping spell and a very high-might creature. So I don't know what to do here.
b. Regardless of if I rule that it is formulaic or ritual magic, the spells would be at least one magnitude higher than the corresponding standard Perdo Vim might-stripping spell, as well as one magnitude higher for each prerequisite.
c. It would require a minor hermetic breakthrough.
d. Depending on how widespead the resulting spells became, and how they were used by both the creating magus and others, it could bring any number of story complications, including charges of molesting the fey/interfering with the divine/trafficking with demons/denying a magus of his magical powers.
In our saga, I thought that, despite his desire to be able to do it quickly, a ritual would be best. It helps prevents turning the world into his vis buffet if he first has to capture and hold the might/vis holding entity long enough to do a ritual. Another PC is an ex-misc hoplite with an infernal patron and goetic arts of summoning and commanding (yeah, yeah, I know) so having them work together on this helps draw the troupe into the hoplite's story arc (the player knows this is a character who may very well end up marched).
Thoughts? Am I being too harsh? Making it too easy?
Thanks for reading
PS - Yes I've read the threads about dislikes of might stripping perdo vim spells in general. Feel free to repeat those arguments here if you must but I'm not going to be convinced. It works for this saga, at least for now. Its what my player wanted. We're all still fighting the learning curve. When we later find the problems with it that you longtimers have, we'll start houseruling more or scrap parts entirely, but at present, since he thought Vim was interesting, we're running with it.