I have a new group of PCs and I'm going to be running the Black Sepulchre for them tomorrow. One issue though, one of them has chosen to be an untouchable and I have some concerns and uncertainties about how that would affect the plot.

Specifically (SPOILERS AHEAD, DO NOT CONTINUE IF YOU WILL BE A PC IN THIS ADVENTURE):

Could the Dei-Phage's hand drain blood from him?

Would the beasts be afraid of him?

Could the shades still interact with him? What effect would he have on them in combat?

Would he participate in the Librarium Nox encounter?

I could rule he just can't be untouchable, but as it fits his mind-wiped homeworld we'd prefer he was able to keep the trait.

His fellowship is halved, and he takes an extra -20 versus anything with a psy rating or the psyniscience skill [he's quite uncomfortable to be around, moreso for them]. So for regular normal animals the fellowship's already doing the job. You can 'show' it by how they act around him, but he's not more prone to them attacking if they aren't psykers in some way, than anyone else with the same fellowship score [and probably no social skills].

As for immunities, he protects a small radius around himself to the tune of -[Trait] psy rating: this will affect accuracy and maximum output of nearby psykers or ones firing at those within the field. The untouchable himself is outright immune to Psychic and Warp effects. Any ability of a Daemon, Warp-Weapon qualities, psyker powers or sorceries or rituals, it just doesn't work. Even inferno won't affect him, despite the giant flames.

I've not read the adventure, but if the blood-drain is physical, like a leech or giant mosquito deal, that will work just fine. If its any sort of power or supernatural ability its going to do nothing. Simply fails. Its not instant but it won't be long before they figure out what the problem is. He won't show up on warp-sight or psyniscience which is a dead giveaway when they take a look.

Entities can still converse with him and all that. Posession and the like wouldn't work, nor would telepathy, but if they can just speak or write, that would work just fine. Not that any warp or psychic entity wants anything to do with the guy.

Rituals though, that gets screwed up FAST. If you can sneak the untouchable into it, things ain't gonna work. Worst case scenario throw him at the main caster or portal or sacrifice and watch their plans go wrong.

That sounds about right. I don't know the adventure, but whether its something a daemon does to them, or something the imperium has them do [sounds like they drew the short-straw of "we'll have to kill you afterwards" expendability], he's not at all welcome in the process.

In fact, they might get a resistance test if they're near to him, despite it probably usually being instantaneous. Like it or not, untouchables really screw up any psyker or daemon plans. They die as easy as anything, but when it comes to this stuff they're, well, untouchable.

The Daemon should be noticibly weaker for his nearby presence though once they're inside. Perhaps give it a -10 to opposed checks, or the party +10 to checks while in there?

As the Daemon is released from his prison, this happens to them by default. If they're close enough (his area of effect is 4m, his WP bonus) I suppose they could skip that part or have a huge resistance to going in. This group is skirting several final encounters at this rate - they sorted out the final encounter in Maggots in the Meat in an unexpected and quite effective way too.

The Daemon itself won't be nearby the untouchable as the others vanish, so not sure how I'd work the resistances out. Maybe a bonus or penalty as long as the untouchable is by his partys bodies, as you suggest

• Could the Dei-Phages hand drain blood from him

Is it a psychic or demonic power?

If it is, then it won't work.

• Would the beasts be afraid of him

Untouchable does not give you a fear rating, and any beast without the daemonic trait would maul a character with that trait as any other character.

• Could the shades still interact with him?

Yes they can even a daemon can punch and untouchable in the face, but any warp powers, psyker powers, sorcerer powers will not work.

Dont forget the particular of…any daemonic or warp entity CANNOT see the untouchable To hit him in melee ( except with a wild random swing IE no hit bonuses ) IT clearly states in the material that the untouchable is not only immune to the warp/psy effects but is also invisible to their senses as well…..

In the Radicals Handbook it says they are immune to all psychic powers, effects, and energy, that psychic powers cast by someone near them have the threshold increased, and that warp instability damage is doubled near them. Daemons are otherwise not mentioned. Light still enters the daemons eyes, surely, so they could see him like that as far as I know. Specifically, it says "He cannot be detected by means of Psyniscience, Sense Presence, or similar abilities." No mention of mundane senses.