Kult 1e. I remember finding a ton of used 90s ttrpgs at a flea market (the original owner's store went bust), and that was the one that really got me. I tried reading it cover to cover to make sense of it, and even as a teenybopper it seemed janked to hell as well as impossible to prep without raw fiat. There must have been something to the idea that trauma, or the character's mental state, literally transformed the world and how they interfaced with it, or transformed themselves in these indelible marks. And like the monsters were also in a way self-reproducing that very state or world. I think it planted a seed in me that I cultivated in other ways but I never got to tackle the thing head-on.

I also want to realise a game of Masque of the Red Death but that's a heartbreaker OSR thing. Heartbreaker OSR things are their own separate thing.