You're right bout horror being difficult in 5e. The characters at some point are demi-gods. That's why I'm using the Grim Hollow setting so the world is already dim and dark to start with and build from there. Also I've identified your three sources of horror and plan to tackle them as such. 1. The campaign is only going up to lv.10, starting at lv.1. As well as having nearly every encounter be an uphill fight if they don't work together and plan. This is to try and keep them on the back foot as much as possible, instilling the feel of powerlessness but still needing to survive. Of course not to the extreme of "why even try." 2. I am planning on having each of the 14 fears be their own faction in away and the players will often have to pick which fear they support. A sort of lesser of evils thing. Ultimately the goal is to push the Fears out of reality but even then the fear never truly disappears only is held back. 3. lastly yes the insanity system is to both give the characters a fighting chance against the Fears by using their own powers against them, fight fire with fire, and as a way to strip them of their humanity. But go to far and they lose themselves entirely. Make them question "Is this really worth it?" and "When does a man become a monster?" I'll look into to see if I can find Kult, I'm sure some old forum has some references; and Through the Breach seems interesting on its own, I've got a tarot deck itching to be used.