I was by a small wooded expense the other day, when I heard something move through the autumn leaves. So I stopped and tried to see the small animal who was making the noise. As soon as I turned, the sound stopped, so I couldn't spot it. So I resume walking, and a moment later the sound happens again. Same routine. This was repeated a few times before I got to the parking lot.
That got me to wondering. Imagine a character walking in the woods, to whom that happens. Again and again, for an hour or so. Don't you think that person would become somewhat paranoid that something (whether a wild animal or someone invisible) was following him?
Now, imagine that this is because the person has somehow acquired an object that is cursed with a magical effect that causes this. It can be hermetic or not.
How would you mechanically describe such an effect?
Rego herbam range sight duration momentary target group is my first thought with a triggering action to activate when the object is moved. You want range sight because range voice won't work with a quiet object. perhaps a special range ie "a few feet from where the holder of the object just stepped" would be better but that would be the same level. Target group would be necessary if you wanted to move more than one leaf (although moving just one might work, albeit less well). So, if my wild guess of base level 3 is right, the effect becomes base 3 +3 sight, +0 momentary, +2 group, no modification for trigger (I'd call movement a regular trigger rather than an environmental one) +10 levels unlimited uses = level 30
It might be more sensible to do create a breeze that blows towards the ground near the item whenever the item is moved, that way you could get by with target individual range touch. Again I'll give a wild guess for base level, this time creo auram level 4. So base 4, +1 touch, +0 momentary, + 0 individual, +10 levels unlimited uses per day = level 15
I'll get the ball rolling, but I'm on the shortest of breaks, and don't have the time to fully flesh it out.
But I'd say an imaginem effect, with a corpus requisite perhaps (to "track" when the person is moving?). Then there'd need to be a trigger -- walking in a wooded area. The effect would be an audible sound. Then you save vs. pesonality traits to see if the person feels paranoid, etc. (this emotional effect would be non-magical.)
The magical shortcut would just be a mentem effect to make the person feel paranoid, with an imaginem requisite. The spell magically makes the person feel paranoid (needs penetration if resisted). They always hear the sound off footsteps, rustling, whatever, depending on the terrain they're in. Since it's a mentem effect, I'd think that the brain of the victim would fill in the blanks, making the sound fit the surroundings.
my 2 cents.