Hello all.

I'm trying to track down which 40K book has the most/best information on the effects of possession by a daemonic entity? Short term, as well as long term.

The character I have in mind will be played using Only War rules, but possession is described very poorly unfortunately in that setting, and my search skills for this forum doesn't yield the information I'm looking for.

Questions such as :

How would PCs/NPCs discover someone is being possessed? (Are there any skills/powers that could do this? I know a good quality Auxspex scanner can based on the description)

How can the entity hide/avoid detection?

Can it enter holy sites through a possessed victim?

What are the long term effects? I read from some of the threads here that ongoing corruption is to be expected, but I haven't seen what sort of intervals we're talking about.

I think it's the Radical's Handbook that has the rules on possession readily available. You can use that as a supplement to Black Crusade if you want to roleplay possession in your own game. I can confirm that this one does have rules for creating daemonhosts as well. Really, it is a pretty good book to have for Black Crusade simply due to the fact that it has so much valuable stuff you can use in a Heretic game.

I've read through the Radical's handbook, and save for the information on daemonhosts, and the daemonhost alternative class, I'm not really finding what I am looking for.

Could you advise further?

How would PCs/NPCs discover someone is being possessed? (Are there any skills/powers that could do this? I know a good quality Auxspex scanner can based on the description)

How can the entity hide/avoid detection?

Can it enter holy sites through a possessed victim?

What are the long term effects? I read from some of the threads here that ongoing corruption is to be expected, but I haven't seen what sort of intervals we're talking about.

1. Psyniscience.

2. I have a vague memory of a "mask of seeming" from the DH book that covers daemonhosts, gives a penalty to detect them with Psyniscience. Otherwise maybe Illusion of Normalcy could be something. Could even houserule that you can do opposed Psyniscience tests to avoid detection (with a penalty, of course — shouldn't be easy to hide).

3. I don't see why not. They can be near sanctified weapons, they just hurt a bit extra.

4. Decide for yourself. There's nothing mechanical for that.