So I am working on a spell that is a bit hard for me to execute. The effect is to make everyone think a particular person is lying that they see or hear. The problem is, mentum does not allow for infectious effects. So the best facsimile I could com up with is this:
Curse of Cassandra
R: Voice D: Sun T: Group
Inclines a group of people to think everything a person, chosen by the magus at the time of casting, says is a lie. This subtly drives the idea into the target minds as well, which could have dire consequences if done in the right situations.
(Base 5 (incline a person toward a particular response), Voice +2, Sun +2, Group +3, requisite +1)
The requisite if for planting the thought that this person is lying into the groups minds in addition to the inclination making the feeling more "real" over the long term. What I was looking for was a means to make anyone who looked on or heard the target believes everything he said is a lie. But imaginum and mentum guidelines don't seem to allow for this kind of effect. I may be wrong but I am assuming that, even with a mentum requisite, species cannot transmit feelings or thoughts to targets viewing it.
A really nice effect. But i follow you that this isn't really supported by any guidelines as is.
In effect you want a spell you cast on - let's call him the "victim" - which effectively makes everybody who hears him think he is lying. So he will more or less be carrying an efefct that does not go off until he is heard. Not really possible. Well, maybe that wierd Mutantum Magic could do it! Tetheres Casting, right? The victim carries the spell and is doesn't go off until a target presents itself. I think the Bjornaer Sensory Magic could work really well for this, by affecting anybody hearing him.
But alas this is not possible by normal means.
It would hav been possible in previous editions. I mean think how Aura of Rightful Authority worked! You cast it on someone, and anybody he gave orders were inclined to follow them. This was an effect carried along to affect people in contact with the target of the spell.
This is no longer possible in 5th ed. A loss sure, but all in all the guidelines make a lot more sense now.
Otherwise the spell you suggest sounds like it could do the trick
I agree that there's no simple, obvious way to do this in Arm5 with "vanilla" Hermetic Magic.
There are a few ways to achieve similar effects though.
One would be to use the CrVi15 spell The Phantom Gift (from the corebook), that "taints" the target with magic making others react to him as if he had the Gift.
Another would be to use "the reverse" of Aura of Beguiling Appearance (from HoH:S), a simple MuIm10 variation on Aura of Ennobled Presence (from the corebook) that causes the target to appear "more friendly, conciliatory and credible", giving +3 to appropriate rolls. It seems reasonable then that a MuIm10 spell could then make the target appear shady and untrustworthy, giving -3 to appropriate rolls.
And note that a magus should be able to "stack" both spells on the target for even greater effect!
Sensory Magic (HoH:MC p27) does that, but the range is Personal.
I think your approach is the best. You could CrMe Estimation "my instincts tell me he's lying" and it would work even if Cognition would have no reason to believe it's a lie. I don't think Rego is necessary though.
Hermetically speaking ezzelino has the approach I'd take: design a spell that reduces how effective the person's communication is, making them sound insincere. A MuMe effect would be fine, even if they say the same thing but their inflection and tone changed enough to undermine the works. Make it slightly higher level and have the target unable to see the difference too.
Thanks for the input. That sound like a good place to start for a younger magus, then build up to Curse of Cassandra, and it does about what I'm looking for early on. There is something to be said about forcing people to react to you in a specific way rather than just making you appear more dishonest. Think of the effects on a magus if the whole turb suddenly believed their master was a lair and a scoundrel. Since the spell doesn't target the magus it wouldn't need to bypass parma, just the Aegis to effect the grogs. This could be a very destructive Wizards War spell.