On page 179 of the core handbook, there is a rule called 'closer than flesh' that states that Telepaths can get more Insanity and/or corruption points when probing the minds of people much more corrupted and/or insane than themselves. My question is whether this applies to all Telepath powers, or just ones that really enter someone's mind. For powers like Compel, Dominate, Mind Scan I fully understand why the rule would apply. But does it also apply to Psychic Shriek, or See Me Not for example?

To me, it only really seems to apply to Mind Scan. But I guess this is up to the GM's discretion more than anything.

I'd say the following powers would need to check

Beastmaster: I don't think, generally, animals can get corruption... but perhaps an evil GM might do it out of spite or malicious joy.

Compel: You're making an opposed Willpower test against the opponents... that implies enough interaction to warrant a check, i'd say.

Dominate: Same deal, but you stay in their head longer.

Mind Scan: Justifies itself, really.

Seed Mind: From one of the splatbooks, this power plants a seed for later, unopposed control. Close enough to warrant a check.

Terrify: from fluff, I'd say it might require a check (You're dredging up the worst nightmares of people with higher insanity and/or corruption than you... their imagination of worst, at that point, could well be insanity and corruption inducing. I'd waver on this one if a good argument were presented.

Zone of Compulsion: Opposed Willpower tests, effectively a sphere of Compel... close enough I'd need a check.

Telepathy isn't on the list, mostly because I don't see any indication it is a two-way street, implying to me a more controlled, less intrusive interaction.

Harsh? Yep. Like normal Insanity gains, they should plateau at some point. I mean, How many insanity/corruption 40+ joe-shmoe NPCs are out there anyway, given that only PC-level folk are capable of withstanding more than a few points of it without mutating wildly or going batshit Khorne Beserker or chant Cthulu summonings?

Edit: By that, I imply that if a psyker has any brains at all, he'll try to refrain from attempting to puppet the guy with the complete set of Hello Cthulu merchandise mumbling something about all the shinies the angels of the new gods brought him. That's where your group Redemptionist steps in and alights all on fire, or the guardsman gives 'em a good Hellgun shot to the face.

Unusualsuspect said:

The exact test of the closer than flesh rule:

If a Psyker uses a telepathic power on a target who has twice his own Insanity or Corruption Points ...

So once you hit 50 IP, closer than flesh won't give you more unless the GM has NPCs with more than 100 IP. Same for CP.