This idea was brought on by my gaming group really getting into Betrayal at House on the Hill, but the question came up about the possibility of having a deck that allows characters to secretly work against each other. On the one hand, a part of me thinks that this flies in the face of the cooperative nature of the game, and I'm not sure what benefits could be incentive enough to cause players to carry out these potential betrayals, while simultaneously keeping to focus of the game on sealing gates to stop the Ancient One. On the other hand, it's not an entirely unprecedented concept, given the Joining the Winning Team card, and the way that investigators' personal stories sometimes require players to act counter to the group in order to not be permanently penalized.

I imagine these cards functioning in a similar way to the Relationship cards, where investigators are given an extra quality, benefit, or handicap. However, these would apply only to their investigator (instead of their investigator and another investigator), and could be kept face-down in order to keep things a secret. For example, maybe one of the investigators can't regain stamina without leeching it off of other investigators in the same location. That's obviously an extreme example, but I'd love to know if anyone has any other ideas for this sort of deck, or if the general consensus is that I'm trying to ruin the game (always a possibility, haha).

That sounds pretty cool. I was going to design one that told the player to "optimize" skills in a manner where upcoming important checks would be failed. For example, max out Luck on the slider (thus minimizing Lore) on the turn where you are going to make a Lore check to seal a gate. The idea was to keep it subtle enough that most other players wouldn't notice that the player was sabotaging the effort.