I am weak when it comes to enhanted devices, and Vim spells, so I was hoping for some criticism and advice.
My players are about to come upon some Mercere Portals, which are locked with similar "locks", but each with a different combination. I am drawing inspiration from a Dr Who episode, where the telepathic combination was "Red", "eleven", and "Petrachor".
However, rather than simple mental images, these portals will need to be hit with a specific Creo Vim spells that emulates components of an artificial casting sigil - ie so long as the Creo Vim spell contains recognisable elements of "crunchy green apple dropped", it will open the "crunchy green apple dropped" sigil lock. Is there a guideline for creating artificial sigils?
This probably isn't going to be too easy to spont for just out of apprenticeship magi, so expect they will build charged devices for each combination they discover.
Though maybe a skeleton key might be made - what would be involved in making an enchantment that created an artificial sigil that the caster specified when they triggered the enchantment?
Altering a Casting Sigil is more in the Muto Vim domain, rather than the Creo Vim. Without the Muto Vim, the casting sigil of an enchanted item (invested, lesser or charged ) would still be the original of the creator.
If a lock requires a Creo Vim with a specific pattern in the sigil, they could have an invested device with the Creo Vim AND the Muto Vim required to activate the lock.
It would not be cheap, unfortunately
Alternatively, they could research a "skeleton key" Creo Vim spell of suitable level, and then spontaneously alter it with a Shroud Magic -like spell.
"Shroud Magic" is a Muto Vim spell to change an exisiting sigil.
I was hoping there was Creo Vim that would generate magic that included a specific pattern. I am assuming the InVi of the "lock" would ignore the caster's sigil component, merely looking for the specific components of the artificial sigil.
Sort of like the "Phantom Gift", but with a complex "pattern". Perhaps I will go with the "Phantom Sigil", which has +1 modifier for a complex "image"?
The problem of CrVi is, that its guidelines are not very refined and do not do finer manipulation. But if you assume, that your InVi looks for very specifc CrVi effects, ignoring other features, you can as well make such a CrVi effect be possible. One assumption comes with the other then.
Legends of Hermes may be useful here - Hermanus of Tremere is in the book as someone who used ReVi effects to trigger magic items, which allowed him to have magical traps that are fired off by other magic items, which were used to defend the Domus Magnus of Tremere. It introduces a ReVi guideline for this.
Off the top of my head, you could also check out the True Lineages book, there's some stuff regarding Sigils in the Guernicus chapter. Otherwise... a Creo Vim spell to put a burst of magic would be tainted by the sigil of the caster. My interpretation of the locks would suggest a Muto Vim metamagic spell affecting the sigil a Creo Vim burst.
Otherwise just creating the sigil would depend on what the sigil is, because a sigil that's the color green would require imaginem, and a sigil that creates actual butterflies (perhaps due to a side effect virtue) would be Animal.
It looks like I may have to change my plans to make the key be either a CrIg pattern of lights, or CrIm image of something.
I had been hoping that it was possible to create a CrVi spell that would create a phantom sigil (along with the caster's own sigil). The other thing is there are some Casting Tablets around, and as we know casting from which will have two sigils, the writer's and the reader's.
My original random thought of "crunchy green apple dropped" was in hindsight badly chosen. I should have picked examples from the main ArM4 book, like Silva of Merinita's sigil of "happy and playful", or the "orderliness" of Ferramentum of Verditus.
Since you can InVi these concepts from spell residue, I had hoped you could manufacture a Creo Vim spell that just simulated such concepts.
I still think it could be done, just not with the CrVi only. Your players would only need to research the "basic" CrVi of lev 3 guideline, and then either research the different Formulaic MuVi Shroud Magic or spontaneously cast it.
I would go towards Thaemir's suggestion' but streamline it.
An invested device can have a feature which allow it to be activated under certain conditions (I believe it is called "Restricted use" - serf's parma, adding +3 or +5 to the item level). It does not require an Intellego spell to detect the triggering condition - there are no explicit limitation to what it can be, so each Saga will have its own definition of what is acceptable.
So if the item's creator wanted a magic item that could be used by several magic users, designing such built-in effect comes to mind. If a given combination of colour, sound and smell had to manifest within a certain order, it can be spont'ed by Imaginem relatively easily (three spont'ed spells of level 5-10), but it is difficult enough if not downright impossible for a non-magic user.
It is like trying a combination lock but instead of having number ranging from 0 to 9, you have infinite parameters to choose from.
I personally like robust but not 100% full-proof limiting system for story: it is hard enough to explain why it was not broken until know (or any conveniently narrative moment), but leave a possibility for a clever NPC to use it (a clever human who had to source rare spice, glass bell ringing a specific tone and precious dye, or bargain with a faerie/demon to have her used her power...). Lots of opportunity for storytelling.
Since I don't want to make the lock too difficult for Spring magi, but do want the "combination lock" not to be easily opened by anyone other than Magi, perhaps I Should make the unlock phrase a sequence of bat squeaks?
basically use a Muto Imaginem spell to convert the spoken pass phrase into ultrasound that only dogs and bats can hear.
Ultrasounds is definitely out of paradigm, however any human phrase converted into any animal sounds through a MuIm will do the trick. "Open Sesame" in seagull screech, or "Thou shall (not) pass miscreant" in bear howling. Just to be a hint more tricky, it might requires an Animalem requisit to be accurate.
Lots of way to customise the opening sequence.
I guess we are entering the area of house rule on how people interpret how Parma is protecting his user and what does it mean to extend a Parma, and can it be done to a non-Talisman object.
For something as tricky as Parma, I would require a InVi to sense it and trigger an effect.
After re-reading the rule (p99), Effect use is restricted to people that can be listed or described in a certain way.
Linked trigger requires that another enchantment is put in the object that will perform the detection (so any Intellego Form that is suitable).
Environmental trigger is specifically triggered by "major magical features of the environment... sunrise, sunset, phase of the moon, etc.).
So if there is a linked trigger build in, you can consider:
InIm 4 (base 1 (use a sense at a distance), +2 Voice, +1 Conc), +5 for the item maintaining concentration.
The item constantly detect with one single sense. If the proper sound/image/odour is done within range, and other effect is triggered (adding +3 to the enchantment level).
You can easily push the detection to two senses being used, for a level 10 enchantment (and still only one vis).
Or you can reduce it to touch range for triggered link to texture (touch) or taste.
You can design an interesting trap that way: to trigger the effect, a person must put his hand into a stone lion maw, with the right food item. If it is the right item, the maw open wide allowing access to what is inside, if not, the maw crushes the hand (it has to be two different enchantments effect obviously).
I wonder if in Medieval paradigm, bats would not be considered to have a supernatural ability to "see" in the dark.
I am always struggling to adjust my understanding of what modern science teaches us and how it would be understood in 13th Century, Ars Magica magical paradigm.