7th edition rules Can Cultists and other characters with 0 Sanity suffer from bouts of madness?

[Merudo]

Can a cultist or other permanently insane character suffer from bouts of madness by seeing Mythos creatures?

And what would happen if a PC cast Mindblast (which causes temporary insanity) at a cultist?

Edited August 26, 2018 by Merudo

[EricW]

There is a case for suggesting cultists and permanently insane might occasionally suffer temporary bouts of sanity.

In HP Lovecraft’s The Horror at Red Hook, the main antagonist experiences a brief moment of sanity when he rejects completion of the ritual which the story suggests might have caused the downfall of the world. In the words of the protagonist;

“He would often regard it as merciful that most persons of high intelligence jeer at the inmost mysteries; for, he argued, if superior minds were ever placed in fullest contact with the secrets preserved by ancient and lowly cults, the resultant abnormalities would soon not only wreck the world, but threaten the very integrity of the universe.”

You could argue that maybe the antagonist never quite hit san zero, and obviously you would have to be careful introducing a flip back to sanity into the rules - it would have to be incredibly rare and transient.

[KeeperXav]

I don't disagree with what is posted above but felt like playing devil's advocate and offering a different viewpoint. In my mind, cultists are immune to bouts of madness. They have been through them many times and come out the other side. I believe cultists trade their sanity for resolve, their core determination to serve or achieve a certain end, and it is only through focusing on this one lone "truth", the only truth that matters, that they can ward themselves from further mental breaodown. They've done it before and beaten it. The ones who couldn't are dead. Or worse.

You raise an interesting question with the spell. If you want the spell to be useful against a cultisr, I would suggest an opposed POW roll with disadvantage for the investigator. Or advantage for the cultist, if you prefer. If  the cultist fails the opposed roll, don't roll for a bout of madness. Just have them collapse, screaming, weeping, clutcbing their head, etc. as their resolve is broken and everything hits them at once. The one truth allowing them to keep their act together lies shattered, and they have no guard against anything. Any cultist surviving this would probably be incoherent, unable to respond to communication, possibly unresponsive to pain, and lacking any sense of self preservation. Torturing them for answers won't work.. They won't even notice the pain or comprehend their situation.

As a side note, I wouldn't allow this tactic to work on wizards. They operate on an entirely different set of rules.