I got the ultimate wildest card for the 'horror-adjacent' IP, it's so crazy it might just work.
Chicago. The iconic musical, which has a movie from 2002 which is widely regarded as one of, if not the best musical movie ever made.
It revolves around the violence seen in 1920's Chicago, as the trial for the murder of a man begins, and the guilty defendant Roxie Hart is defended by the slimiest and most dramatic yet greatest lawyer ever, Billy Flynn.
Can argue that it's horror-adjacent with all the murders that happen, and the large amount of iconic scenes that can be put in can make for an entertaining house.
(...yes, I'm very well aware there's a 99.99% chance it isn't Chicago and I'ma likely get a lot of flack for this, but hey, I think we've had wilder guesses for what this IP could be.)