ARISA
Not exactly horror but it has many plot twists and kinda similar to "Ousama Game". Features less gore and more suspense. The art style is a MAJOR PLUS, I like how the mangaka used cute, shoujo drawings and turned them into one creepy, mystery story.
Franken Fran
Multiple stories, each with a plot twist at the end. MC is a hawt female version of Frankenstein. Very gory, imagine 'mad scientist performing gruesome experiments on her clients' only this time, the protagonist does so for the sake of 'helping others' and not for spreading terror in humanity.
Tokyo Red Hood
A very disturbing, twisted version of "Little Red Riding Hood". I dropped this early on but I plan on finishing it some other time. Not a big fan of the art. The gore is good tho, and the mc's messed up in the head so it ain't all bad. It's about a little girl's quest on finding "Mr. Wolf", whom she fantasizes on devouring her.
Hanako to Guuwa no Tera
SPLENDID! I thought they're just multiple stories but it ALL ADDS UP in the end. Definitely one of the BEST, storyline was done so well. Rec this one to those interested in Japanese urban legends and horror stories with a bit of romance ^^ The ending makes me want to read again. It's the same author from "Future Diary" so why not? :)
Worldend: Debugger
I thought of taking a break from yaoi BUT THIS MANGA BE LIKE, "nuh-uh." BTCH WHY THERE NO UNATTRACTIVE CHARACTERS >.< I want more death games and gayness people!! #ROHOMOisLIFE
Seeking for Death