Here is a glimpse of one of the sections of Strange Tales New England, to give an idea of where the game is heading. This is just a rough section of GM advice. We started a regular campaign in the fall when I started work on it and the example is from that campaign (which is still on-going). The character Letha Kane in the scenario is was an homage to the Ninth Configuration.
BENDING REALITIES AND THE UNRELIABLE GM
Reality bends around the central mystery of your campaign and of the conceits of the setting. Player characters may not be who they believe themselves to be, they may mistake friends for monsters and attack or kill them, they may find themselves lunatics in the asylum. The point is psychological horror. And the GM’s role is to intentionally confuse while at the same time offering real choices.
This portion of the game is meant to be very fluid and surreal. The GM should use judgement in presentation of such things. As a general rule, when a player is subject to something false and you believe there should a chance for them to see through it, you can roll 1d10 against Wits and have the delusion fade if the result does not meet or exceed their Wits score. In many cases though such a chance will not need to exist.
When reality is bending, when players are the subject of illusion, false memories or delusion, use the unreliable narrator approach to GMing. This takes a certain amount of care. It is a delicate balance, to mislead while also maintaining the trust of the players. As a general principle, when you are being intentionally unreliable try to be subtle, but also try to include the possibility of the players sensing clues that they are being misled. This technique should also be relegated to things specific to this part of the game. For example when players are venturing into Danvers State Hospital or when the reality of their past lives are unfolding, playing with the truth about who people are, what happened, etc can be helpful. The idea is what the players are seeing and what the NPCs are seeing may not be the same thing.
How this was handled in practice was very much about presentation of information and techniques like artfully switching between groups of characters when they were split (to maximize the impact of information being revealed). In one playtest I ran, the party went to Danvers State Hospital to investigate an inmate who had committed murders that one of the players had dreamed about. Before the campaign began, I rolled a 1 for him when checking for Lunatic Player Characters and slowly started connecting him to a secret past involving this inmate, which came to a head for the player while investigating werewolves near the scene of his original crime. At the hospital they were told this player, Daichi, could interview the inmate, Peter, alone. They agreed and Daichi went to Peter's cell to interview him while the rest of the party went to another area of the hospital with the Physician who had greeted them, Dr. Letha Kane. It was slowly revealed that Daichi was in fact Peter, that he had escaped and they just returned him to his cell. But this was a slow process of revelation. Daichi spoke with Peter, getting pieces of information that started to persuade him he wasn’t who he thought he was. Peter would say peculiar things like “but don’t you remember?”, or “I didn’t do it, that was you.”. I would shift back to the conversation with Doctor Letha Kane and she would begin describing Peter’s multiple personality condition. This went on until it was revealed to the party that Daichi was one of Peter’s personalities.
It is a somewhat cinematic approach but requires a great deal of care still respecting character agency. For instance, only Daichi had rolled a 1 on my check. The other players were fully aware of things. I had permitted a certain amount of illogic and dream logic in the timeline, because this was purgatory, but when they concocted a plan to bust Diachi out of the hospital, the campaign went in that direction. And it was unclear to them for some time if they had been lied to, enchanted by, or told the truth by the people at the hospital.