I think the most horror oriented drug experience was on ketamine + N2O + weed with my friend reading from Dante's inferno and showing me the brilliant illustrations by Gustave Doré. I wasn't afraid because i was dissociated, but the content was impressively horrific. That book is something special, as are those illustrations.
The emotional confrontation of mushrooms is more frightening, but less stereotypically scary.
I also had a very frightening episode on just weed after a 2 week break. That anxiety is hard to describe. I believe weed has a very sinister dark side compared to psychedelics, although less overwhelming.