One recurring theme in my games is the concept of transferring the life essence of a being into an item in order to power magic in the item. It is powerful, and evil, approach to magic item creation.
I have been pondering how to translate this to Ars Magica. A few ideas:
Investing any item requires only 1 life essence. This removes the restriction of max vis based on magic theory
Concentration "for free" - the trapped essence can maintain the effect(s)
Reduced costs for triggers - the trapped essence can detect the trigger and act accordingly
Shape and material bonus for lab total for effects related to the life essence transferred
In addition to trying to figure out the benefits, I have been also trying to figure out how magi could learn how to do this. Would it be a mystery that leads to a supernatural ability that enables this approach? Would it be a hermetic breakthrough as an alternative approach to enchanted items? Some other technique? I must admit I am partial to the supernatural ability approach because I like the idea that success is not guaranteed.
Any ideas/thoughts on the bonuses and method of learning this approach to creating magical enchantments?
You might take a look at the Verditius Mystery 'Bind Magical Creatures,' found in HoH:MC 134. This mystery allows a Verditius magus to power enchanted items using the Might of a Magical or Faerie creature. Whatever you decide to do for mundane beings, it should be LESS powerful than that.
In particular, I don't recommend allowing the sacrifice of a single life force to prepare any item for enchantment. Anything that open-ended is just asking for your Saga to be broken. If you want to waive the Magic Theory limit, that's one thing, but perhaps each sacrificed person counts as only 1 pawn of vis. You might allow the magus to add some kind of Infernal or Cult Lore to his Magic Theory for this purpose, rather than waving the requirement completely.
Another guideline from ancient magic- fertility totems- they have to be crafted by a woman, can be used as a focus for a bonus in fertility rituals for that woman, and contain one pawn of creo vis that, if harvested renders the woman barren.
Aside from that confidence seems to be the most common form of vis conversion- in some cases it can be a combination of sanctity and confidence to create infernal vis when an object is desecrated, or in ROP:M an entity with vis mastery can convert confidence directly into vis. ROP:Faeies implies that each experience point from an adventure can be converted into faerie vis.
Their are actually a few clever schemes to create vis with mass murder. Fertility cults can create a decent amount via mass production of children. While technically not mass murder, you'll want to anyway to cut down on mouths to feed. With a little mind control and forced maturation each baby girl is a corpus vis. The ghost a person leaves behind is a good source of vis. Summoning ghosts can be done en mass with group targets or the like, then the ghosts rendered down for vis. You'll turn a profit in the end.
Maybe 1 vis from each person is a good exchange rate on that basis with the right abilities.
My opening gambit? For each -1 (or is it +1, I can never remember) penalty to their Aging roll, you power a device to the tune of a pawn of vis. The maximum size of the penalty you can give any one individual is going to be tied to your lab total (probably PeCo as an inverse of the longevity ritual). When that individual dies, the enchantment(s) powered by its life essence stops working.
So I'd look at the aging roll penalty as the basic unit and build a system around that. It's dangerous enough that the effects might be really unpleasant, but it has the advantage of keeping the "donor" around for a while for all those moralistic stories.
I may be mistaken, but wouldn't that process turn the PC into the new Diedne heretics ? That would be a pretty big drawback for the covenant, especially knowing that there are still some Tremere and Guernicus magi looking around. The PCs would perhaps even be forced to suppress the occasional magus that found out what they're doing, making the secret even harder to keep.
That could be a good theme for a horror-themed saga.
From what I read in the OP, we are talking about something "evil" that involves human sacrifice. Diedne may or may not have practiced that, but they were certainly accused of it, and whether or not the new PC covenant is Diedne or not is irrelevant to the fact that they're going to be hiding from Quaesitors.
Yes, I meant the new Diedne as in that they will be targets for lots of people as soon as anyone knows and lives to tell about it. Also there are still people searching around for people doing what they do (the Burning Acorn Vexillation, probably some quaesitores too).
Consider that transferring life essence into an item isn't evil, but the methods for doing it are? For example, to transfer life essence, you have the have the individual being transferred agree to the process. That agreement is probably acquired through extended torture and other coercion or manipulation. It leaves open the idea that someone could sacrifice themselves for this process, if everything is explained honestly and without torture. It's the rare circumstance that it would ever happen, but it is an interesting conceit. It's not about about the destination, it's about the journey.
I'm of an opposite mind, I like the idea that it is guaranteed. I mean, if you're going to sacrifice another human, you want something out of the deal, and you are probably pretty sure you're going to get what you want out of the deal, otherwise, you do something else that is less risky than human sacrifice.
I am not sure the 1 person=1 vis will work. I am looking for a better trade off between reward and evil. But imposing a cap per person sounds like a good idea.
I had not thought of using Confidence. I like that idea. I could also give a bonus for supernatural or hermetic virtues and flaws. I could combine that with the practitioner's cult lore skill to determine the max vis from a person. So a lore skill of 4, confidence of 1, and 4 supernatural and hermetic virtues/flaws gives 9 effective vis for the item.
I also really like the aging roll approach. It opens up a whole new set of story possibilities.
It seems like either approach would be a supernatural ability and hence need an initiation script? And that script would be experimental since the cult/ability does not exist yet?