I read your last letter a few times before it finally hit me. I'd been so stuck in looking at wardings based in some standard energy, but now I realize that may not be necessary. There are plenty of schools of magic I've left untapped, and the likeliest candidate right now seems to be a combination of a couple of effects.
When you mentioned that the masks can create a limited forgetfulness, I was reminded of an effect I read about in one of my roommate's old school texts. He's never been much for these sorts of effects, so it was only by sheer luck that I'd found it on my own. Certain mental mages who also specialize in illusion can do a variation on a basic invisibility illusion that depends on the subconscious compliance of the observer.
It's an effect that causes a targeted person or object to repel an observer's mind. Unless the observer is specifically and actively looking for the object, it's like it's not even there. Now, there is a minor problem in that I have little to no expertise in either illusion or telepathy. Certainly not enough to experiment with it that way. Not directly. However, based on a few elementary principles I could devise an experiment with another caster.
This would be an extraordinarily useful effect, and could be related to the workings of the mask you mentioned. A couple of changes would need to be made. For one thing, I would need to apply it to an area and not a person or specific object. For another, it would need to be keyed solely toward incorporeal undead, or else I'd become hopelessly lost inside my own lab. That would be a pain.
This is where things become a little sticky. I do happen to be acquainted with someone who can create illusions on that scale, and while I'm a little concerned about seeking her assistance, I think I can convince her to assist me. Her name is Sadie, and she's extremely skilled at creating illusory landscapes.
The problem is that she's a ghost I knew when I was young. We had a brief falling out several years ago after which my familiar nearly destroyed her. Since then she's cooled down a little bit, and I think she would be interested in this if only to take away some of my dependence on my familiar (whom she, like many ghosts, dislikes fairly strongly). If I could explain to her what I needed her to do, she might be able to hide me from other undead by adapting her normal tricks.
Now, if she's able to do that I'll know that I have someone around who can duplicate the effect on your mask. That's step one of several, really. My mind is racing; I just have to get all this down. If she can hide me from other ghosts-- which I think I can help her do-- we could potentially tie the effect to some sort of border instead of using her as its center. Sadie is the type to use it to create some form of persistent playground from which we could leave and return, and that may be the best start.
Next hitch? Sadie was never tied to me specifically, and summoning her to my lab might even be a little dodgy. If I break her connection to her bonded location, ensuring that she ends up with me and not... anywhere else in creation could be... a little dodgy.
This means I have to go back home. She's tied to my grandfather's house in the Netherworld, which means that's where I'd need to be. The energy balance on that plane tends to be a little different, but the higher saturation of shadow energy has made my work easier mechanically even if ghosts tend to give me more trouble.
I mentioned to you in a previous letter that I plan to use my own condition as an opportunity to learn more about the management of possession, and that I needed some sort of energy-neutral barrier to contain any problems I might cause. That will give me a little more freedom to work, and is absolutely essential to some long-term goals I'm working on.
I would never have thought of this without your assistance. I really appreciate your advice on this, and I can finally move past an obstacle that's been plaguing me for some time now. I'll be leaving this address shortly to pursue my work elsewhere, but written on the back of this sheet are instructions for getting correspondence to me at my grandfather's house. As you can imagine there'll be a substantial delay, since the interplanar post is not quite as reliable as one might like. If nothing else, I'll contact you when I've made some progress.
Thank you again. You've been absolutely invaluable.