Firstly, I'll admit that my knowledge of Untouchables essentially stops at the Culexus fluff from the latest codex and the awesomeness of Alizebeth Bequin in the first three Eisenhorn books. I've noticed that players and posters online seem to have very different ideas on how exactly they work, so I'm a bit puzzled.

However seeing as I'm currently playing one (and a mutant one at that!), I have a few questions:

1. Are there any main things about the portrayal and effects of Untouchables I should know about? I've seen them described as causing headaches, being seen as "walking voids" by psykers (and for the Culexus, sometimes even invisible to normal humans!) or even normal humans that are just considered "odd" and unnerving for some reason.

2. Can Untouchables gain corruption in the fluff? Mechanically I have 10 points from my Background, and I'm wondering how that works seeing as I am some kind of anathema to the warp and have no soul to corrupt. Did I miss a rule somewhere?

3. The whole "no soul" issue: what happens to me when I die? I suppose I don't go see the almighty Emperor - but what about the Chaos Gods?

4. How hard is it to hide an Untouchable from a psyker? Can they recognize me immediately? Can they sense me through a wall? In the middle of a crowd?

5. The game differentiates between many differing levels of untouchables, such as Untouchables that somehow affect Daemons, Untouchables with AoE Psy Rating reductions, Untouchables that simply cannot be targeted or affected by most powers (80+ Deny the Witch baby!).

6. Is there an actual difference between Pariahs, Untouchables, and Nulls?

1. The effects vary, but it boils down to normal humans just not liking them and psykers feeling pain for going near them. It ranges from Alizabeth (who is just disliked by almost everyone for no apparent reason) to Gunner Jurgen from the Ciaphas Cain novels (who is always flithy and smells terrible, no matter how much he cleans up, which is rarely).

2. Corruption impacts the body as well as the mind, so Pariahs still suffer from it. It's even in the FAQ. In-game this is probably for balance reasons.

3. No soul means you are just gone when you die, so the Chaos Gods can't turn you into a plaything after your death.

4. Once the psyker gets close, they will start to feel the effects. If this psyker, or one of their handlers, is aware of what Pariahs do that will blow the Pariah's cover in seconds. I doubt they could sense them (or feel their effects) in a large crowd or through a wall that's thick enough. The Ravenor novels did mention a limiter that essentially turns off a Pariah's anti-warp field, but that's not stated in game. As a GM I'd use this rule: If you get close enough to have an impact on a psyker or a Daemon and they know what pariahs are, they will single you out and realize what you are.

5. Not all Pariahs are created equal, just like psykers they have different levels of warp-negativity and they can also grow and develop their powers (in-game by buying the talents you mentioned).

6. The terms can be used interchangably,

I dont own this game but I do own Slaves to Darkness and The lost and the damned source books from yonks ago.

The way it was described was that everyone has a presence in the warp. For most, this is just like a tiny pinprick of light - it doesnt attract attention. For Psykers, the light is a flame attracting predators. Untouchables (and the children sired by the Emperor) are completely dark in the warp, meaning that they just arent affected by any warp fuelled activity. Even the Emperor himself is blind to his own children and they are oblivious to their father. These guys (sensei) can use and mould the warp to do their bidding also though and can become the equivalent of daemon princes.

The illuminati seek the sensei under the guise of protectors, but the eventual plan is to offer them up to the golden throne on the day the Emperor finally gives up and to sacrifice them to re-energise the Emperor.... Did I also mention that they live forever (unless killed by someone)? Sorry, I am going off topic....

With regards to question 4, I guess the effect would be a blind spot in the Psykers sense. He probably wouldnt notice the disturbance in the psychic background unless he was faced with it or it was close by. Even Cherubael only discovered Alizabeth was a blank when he was close up and personal. Im guessing most psykers have never met a blank.

Incidentally, those who have no presence in the warp are/were hunted down and rendered into ammunition used in psy cannons in the original fluff.

The incidence of Untouchables in humanity is very, very, very rare. Something to the tune of 1 in 1 billion, if I am not mistaken. There are a lot of humans in the Imperium, but that still means there aren't that many Untouchables - any old psyker probably has never heard of such a thing, let alone encountered one.

People in the Imperium are taught to abhor the witch. I seriously doubt they are ever taught that sometimes, humans are born without a soul and the Emperor's Light can never reach them. Why would anyone advertise that there are some even the Emperor can't reach?

The incidence of Untouchables in humanity is very, very, very rare. Something to the tune of 1 in 1 billion, if I am not mistaken. There are a lot of humans in the Imperium, but that still means there aren't that many Untouchables - any old psyker probably has never heard of such a thing, let alone encountered one.

People in the Imperium are taught to abhor the witch. I seriously doubt they are ever taught that sometimes, humans are born without a soul and the Emperor's Light can never reach them. Why would anyone advertise that there are some even the Emperor can't reach?

Rarer than that even, I think the rate is 1 or 2 Pariahs born per generation on Hive Worlds (so like 1 in 10 billion or even rarer). And most of them don't survive long because every hates them and brands them mutants or just kills them/neglects them because of the null field.