Demons as manifesting spirits

[Kissamies]

So lets assume a cosmology where there's the material world and an astral plane that is parallel to real world. The astral plane contains all sorts of spirits, though few are actually native to it. They come from various metaplanes instead. Demons come from a some sort of hell, for example. The astral plane is easily accessible from many planes, a sort of crossroads. From the material word is accessible by becoming insubstantial, projecting, or similar methods. Vice versa, the spirits can interact with material world as insubstantial beings do, if they can materialize and so on.

Now demons are spirits. They can materialize, but only with assistance. Either by a Summon Demon spell or something similar, or a patron deity. In latter case, the demon can manifest anywhere the god holds high sanctity. Most demons don't like serving gods, so they spend a lot of time trying to manipulate mortals into summoning them. Demon's physical from can be destroyed relatively easily, but this never kills them, merely knocks them back to insubstantiality, maybe banishes them back to the home plane as well.

In actual game I could just treat them as material beings like in M155, for example. No real need to stat the the spiritual side of them... Depending, of course, on how much the players would interact with that. However, I am curious about how exactly one would stat this. Some ideas:

- Basically a spirit meta-trait on Basic Set or Fantasy, but the Insubstantiality needs tweaking. A limitation like "Needs assistance to materialize". -20% perhaps?
- The physical form is easily severed, which means Fragile (Unnatural; Only when materialized -20%) [-40]
- However, destroying the physical form doesn't kill the demon: Unkillable 3 (Only in material form, -20%) [120]

Sound reasonable? Other ways to handle this, with Alternate Form perhaps?

Edit:Found this thread: http://forums.sjgames.com/showthread.php?t=35192
Helpful because this is partially inspired by 3e spirits anyways.